May I wish you a warm welcome to the CameraLabs forum.
I've used an SMC Pentax 67 165mm f/2.8 in front of a dedicated CCD sensor with limited success and that was using separate exposures for red, green and blue. Your EOS sensor will have smaller pixels which will be even more demanding and, worse, any lens you use will have to be extremely well colour corrected as you'll likely be taking RGB exposures rather than separate red, green and blue ones. Colour correction would be a concern to me with an infinity focus FD adaptor but I've never tried one so I don't know how good or bad they might be.
In theory you could use any lens that has a flange focal distance equal to or greater than that of the EOS system (there's a handy table here
) provided you can source a suitable adaptor. The trick is finding an exceptionally sharp well corrected lens that is no longer usable on modern camera systems without an adaptor but they are few and far between and it can be hard to track down reliable reviews even when you think you've found one because often they predate the widespread use of the Internet.
When I used my 5D2, now sold, for astrophotography one of the big advantages of using Canon glass was the ability to focus remotely using the EOS Utility software. It might not sound like a big deal but trying to focus my Pentax 165mm f/2.8 lens accurately by hand is a right pain. The amount of movement on the focus ring to go from perfect focus to unacceptable is really small!
Bottom line is that if you can
run to EF glass then do so. So long as it works and the optics are good it doesn't matter what state the lens is in cosmetically so you might get lucky. Hope you do...