Hey Milo! Here’s a few thoughts for your consideration.
The Clark transaxle was made by Clark solely for the Cortez. To my knowledge, it was never used in any of their other equipment. There weren’t a lot of Clark units to begin with, and the number of units left is regularly shrinking. So finding a replacement transaxle may be VERY difficult. The manual for the transaxle is pretty good, but you’d still need to find some sort of old school trans shop who’d be willing to work on it and find/fabricate parts. There were a couple of guys who did Cortez trans work, but they are retired and/or passed away, so that knowledge may not be available either. There are no off-the-shelf parts, such as synchros that I’m aware of (I wish I knew the answer to this).
You cannot simply swap in a Kent drivetrain. It actually takes considerable fabrication to make it work.
So, if you buy the non-running coach, you are taking a chance that there are trans problems, that could be difficult to cure. On the other hand, I’d hate to see it go the way of so many others.