New components replace all those which are second hand on the car when bought and which may be not "as new" : engine, tires, material top, front seats, rear seats, front or rear fenders, floormats, felt on the inside of the body sides and soundproof foam around the dash.
All those components are let "as is" when you buy a 2CV on the lowest end of the price range and want to refurbish the car yourself as a hobby.
They are replaced for new ones on request according to your needs and budget.

Better than new components are the following :

New engine, 0 km, out from the box
The mileage of a second hand engine sometime cannot be known with accurate precision. Most of the 2CV engine however can last and, even very old, can still run strong but you have to be carefull with the oil feeding.
If you just want to use your 2CV from time to time, a second hand engine is OK.
For extensive daily travels, a new engine is better : you know exactly the mileage and, if you regularly change the oil, it will last up to 80.000 km without oil consumption then will still be strong for years with only a normal oil consumption.

Repaint
A respray is cheap but is not a repaint.
A few words are necessary about paint.
Too many people think a respray (called voile de peinture in french) is cheap.
A respray is cheap but a respray is NOT a REPAINT. A respray is done in one day in your garden by sanding the surface then spraying the paint with some tape on rubbers and windows.
For such a work, what about the lasting on time, the shining, the slickness, the border of the rubbers, the rust spotted areas ? If you have chance with the temperature, you may have a good shining on most surface but, excepted if you are very lucky, you will have areas where it will not shine because of a more or less rough surface and because the whole surface is not at the same temperature when you paint and may, in addition, not dry at the same temperature.
The garage Gilles is equipped with a painting room. In a painting room, the temperature is controled, so shining is allways perfect because all surface is at the same temperature and dry at the same temperature, 20°C, whatever the outside temperature.
In your garden, or home garage, you will also always have the paint fog falling on the paint, when a painting room have a vacuum system under the floor to remove that fog as you are painting, insuring a good shining again. A painting room also have filters to remove dust, something you do not have in your garden or garage and which decrease the quality of the painting.
Another point is that repainting on sanded paint is not enough to insure a good grip of the new paint. Of course, the grip will be good for the first six months (long enough to fool a potential buyer...) but after that it may go away, usually starting around the rubbers.
A professional repaint starts with a sanding, treatment of rust spots then a first coat of primer, a special paint designed to grip the old paint, fill the small defaults and grip the new paint. This primer is sanded, very smoothly (p800) then the final paint is sprayed.
At the end, there was in fact two sandings (old paint + primer) and two paints (primer + new paint).
All these features will clearly make a difference between an amateur work and a professional work, that is a paint which will vanish and one which will last.
A repaint with strip down, sanding, primer coat, sanding again then painting in a paint room is the same cost whatever car you work on : a minimalist 2CV, any Renault, Mercedes, BMW, a Rolls Royce or a Ferrari.
The work is the same, so the cost is the same.

Hot dip galvanized chassis
The chassis is very sensitive to rust. During the last years of production, it was sometime even not painted ! A 2CV can have the chassis completely made despite a perfect body and a good engine.
When the chassis is made, there is no other solution than to change it : due to its design, a 2CV chassis cannot be fixed safely (unless stripping it down but then it is cheaper to change it for a new one !)

Be extremely cautious if you are said things like "2CV frames usually have to be welded every some years, when you bought a brand new Citroën 2CV, you got the rust as free upgrade"
The 2CV frame is not shaped as a six sides box : there is an internal structure and this is this structure which gives the rigidity to the frame. If you need to weld patches outside, you probably also need patches inside because of rust. But the inside is unreachable. So a welded chassis is a weeked chassis with hidden internal damages : go over a bounce too quickly and smile when your 2CV collapse because the chassis bent just behind the front wheels !
Rust comes from a lack of rustproofing, that's all : rustproof what is needed and here you will have a safe and lasting chassis. All 2CV bought from us have the chassis rustproofed inside and outside prior to shipping.
The best solution however is to choose a hot dip galvanized chassis : it will never rust.
A rustproof coating can be added, mainly inside, not for rust protection, but for reducing resound.

Inox steel exhaust line
The exhaust system can rust away within two years. If you use the 2CV only for short trips and from time to time, the lifetime of the exhaust can decrease to no more than one year. This comes from the fact that the engine not only produces carbon dioxyde but also steam. When the exhaust is cold, the steam produces water. If you drive your 2CV for a short distance only, the exhaust have not enough time to warm and evacuate water. As a consequence, water stays in the exhaust and quickly destroys it.

With an inox steel exhaust, no more rust problem.

The whole line can be changed for inox steel but at least I would recommend to have the first muffler changed. This part is not easy to change as you will have to lift the front of the car (where is the engine-gearbox assembly...) very high to be able to remove the part from under the gearbox.

 First tube

Second muffler

Second tube 

Electronic ignition
Why an electronic ignition system? When a 2CV does not start in the foggy mornings or when it runs badly, this usually comes from a wrong adjusted timing or from burned out contact. The ignition breaker is subject to a great deal of wear and tear. You have to change the breaker between 20-25000 km (12-15000 Miles). Only a few 2CV have this preventive maintaining. When the ignition timing becomes out of range, the power of the engine decreases, the gas consumption increases and the engine is unwilling to start.
The main difference between a normal ignition and an electronic ignition is that the coil current doesn't flows across the breaker.
If the electronic ignition is using the original point breaker, only a little control current runs across the breaker, giving it a much longer life.
The main current is switched on and off by a transistor which does the job much better than the breaker, producing a better and stronger ignition-spark.
This has three important advantages:

• Because there is no longer a current of more then 3 ampere at the breaker it lives much longer. A lifetime over 50000 km is normal and up to 100 000 km is possible.
• The power of the spark is increased. The engine runs more gently and is easier to start.
• The timing is constant. The engine always has perfect timing, you don't loose power nore waste gas.

Both kind of electronic ignition are available as an option for your 2CV.

Module using breaker. Going back to the breaker is possible by unswitching the module.		Module not using breaker (magnet) Going back to the breaker is impossible unless you swap the whole breaker box.

I recommend the VARIBOOST1 electronic ignition. It is not an industrial product (it is home made) but the designer and builder is both an electronic engineer (Motorola) and a 2CV driver with numerous travels in Europe, Africa, Canada, South America... (quite only USA is missing so far !) so he knows what he is talking about :

Extra-power engine
The first significant step to a stronger 2CV engine is the 650+cc tuning (instead of 602cc).
The engine power increases from 28-29 HP up to 34-36 HP.
Your 2CV will be almost unrecognizable with this little implant. Bigger tunings are possible but decrease the life expectancy of the engine. Also, it is not safe to have a bigger engine and go faster if you do not have enforced brakes, enforced transmissions, enforced clutch and so on...
The Citroën factory produced a derivative engine from the 2CV engine for their VISA car and this derivative engine was 650cc. As a consequence, the 650+ step is the best choice.