My guess is that if you get the front shaft and crossmember from the
donor car you will be in good shape. That is what I did and although I
had to do a bit of finagling with the center bearing mount (the last of the
old style) it went together OK and I am still using it.

So in your case I would get it and go for it unless there are condition
problems.

I'll let someone else tell you about the prop shaft - I've alway had to shorten mine. Re condition: Aside from making sure everything turns smoothly, there isn't a whole lot you can do beside checking for leaky seals, sloppy shafts, opening the gearbox to check for obvious wear and bits of metal sunk to the bottom. On the OD unit, unless you want to dismantle the whole thing, look for junk on the filter and magnetic strip, both of which you reach by removing the bottom plate. Remove the solenoid and test it by touching 12 V to one contact and grounding the other, you should hear a distinct click and the piston should move with conviction. Then shake the thing vigorously and listen for it to rattle - no rattle, no good, lots of $ to replace. Some better men/women than I have managed to open them up and fix them. I've never been able to even get the casing off. If all seems well, and you decide to buy the thing, at least, replace the gasket on the bottom cover plate, the output shaft seal, and all the O rings.
Good luck,
Bob S