Engines will both be small block fords. If your grab an exploders engine and tranny, you will have an Auto ( they didn't make a stick/v8 ).
If the stang is trashed, snag what you want from it and save some cash. If you sell the stang, you'll have some cash but starting from scratch.
It works either way, I went and built an engine, came from a friends 92GT. Still in the mix of my project. Its a fresh engine whereas if I bough one, I wouldn't know its history/beatings its taken.