I assure you, all Fox bodies that had door speakers from 84+ have 6.5" drivers in the doors. Mustang, T-bird, Cougar, Mark, LTD, etc. . .
As for the rears, you can find drivers that are marketed as 5x7/6x8. These are essentially a 5x7 with additional mounting holes that fit 6x8 mounts. Some are slightly larger so they will not fit a traditional 5x7 opening.
'87 Turbo Coupe