Loose fitting of any system is always the way to go,so you can jiggle it about to get all your mating joints right, especially the flare and taper at manifold and heat exchangers on a 2cv. Ideally you want no stress at any joint other than from the clamps. So when it's all tightened up the rubber hanging points are just that ,hanging and not under any strain.
Just to illustrate the point I've had a couple of K100 BMW bikes which on the earlier ones had a habit of breaking the exhaust just where the four pipes enter the silencer.Once I'd got the system off as a complete unit pipes and silencer. I could see that the cracks radiated from the short stubs on the silencer. I brazed these cracks to fix and as I offered the system back up you had to force the system up to it's two rubber mounts on the silencer.I already knew that there had been fractures of that mounting plate recorded..I made a plate that allowed the system hang from the rubber mountings without any strain.The repair I made by brazing is still good some 12 years or more down the line,which surely would have failed if I'd put it back as per factory..
