1974 AMX Javelin

Not familiar with those rigs, hard to advise, but I would not want the weight of the transmission on body surfaces while towing and bouncing around. Isn't there a frame member or suspension parts in there you can engage to support the trans? Maybe say, cut a 2x6 the right length to span the frame horns in the bay, then drill it to engage some bolt holes in the bell, and stick some long bolts or threaded rod through?

I'm not sure spending time putting the engine in is wise, you'll likely want it back out before final install.

I always kinda liked those body style