Seem to remember a very good article in the Citroenian many moons ago that gave chapter and verse about CX driveshafts, including the identifying rings on the shafts, to ensure you had the right one.
I'll see if I can find it.
Failing that, give Stan the Man a call as he knows everything about CXs and he might even have some driveshafts available.
GTi T2 5-speeder box fitted onto DTR2 Safari with no driveshaft issues
and I've seen the reverse conversion too. Shouldn't present any issues
apart from ABS teeth but reluctor rings of differing teeth and diameter
are available in many sizes which could make a new sans teeth
driveshaft work.