they are really tight to unscrew when they are not corroded into the drive .

They will unscrew but I'm not so sure there's enough stud sticking out to put 2 nuts on there. There's only a couple threads sticking out of the nuts normally. The wood trick always worked great for me. Another way is to put a small piece of 2 x 4 between the top of the drive and transom assembly and run the trim cylinders out. Who knows he might have it off already.

Personally i wouldnt touch the studs theyve been in there for what 20-30 years depending on the year of the transom assembly. Soak with PB for days if you have to and heat it.. it will come off.

Worse case, I had the same problem, I backed the boat into a wall and hit the trim switch and it pushed the drive off, make something out of wood to cover the prop shaft so you don't bend it, let the case take the load. This is after everything else has failed and it could break the gimble and/or bell housing.