Your comment reminded me of this video I watched recently.Drivetrains are cheap, due to all the rusty cars, and rust repair is expensive.
If there are huge gaping holes, then getting it running/driving/stopping probably won't get you more money. Not from anyone that knows these cars.
Virtually anything can be fixed, given enough time, money, skill, and proper tools.
Normally, the cost of any such restoration greatly exceeds the value of the final product though.