I "sorta' know". I think they're a bolt in. I have done the oppisite and put the highbacks in an early car that came from a ''71 Mach 1 so it would make sense that the early seats would just bolt in to the later cars.
Love hard, drive fast, wear your seat belt.
PS, that's my 'bird...... My Mustang is too ugly to take pictures of yet........*G*.