These seats fit great! And they feel great -- in my winter-garaged '66. Gotta wait 'til Spring to get on-the-road seat time. Straightforward install: 07 Mustang seats into a 65 Mustang!! - MustangForums.com With the 3/4-inch spacers described in the above link, I gained an inch of...
www.vintage-mustang.com
Yes. "Most" seats will fit a classic mustang...pull out a tape measure an measure the seat bottom height and the bolster height to know for sure. Its more a matter of modifying the seat rails to fit a given seat. I had some foxbody seats in my old 67 coupe....but the floorpan(and therefore the basic interior dimensions) are the same from 64-70, I also had Fiero seats in my last '66, and those are nice because of the in-seat speaker option:
MrMikes.com offers re-upholstering for fiero seats to be used in a mustang, although I don't think he uses the original vinyl colors, so finding a match may be difficult...or you may have to send him some material to match, you would need to ask him.
I myself plan to use 1st gen Capri seats in my current mustang:
I like the Capri seats best because they look very close to stock with significantly better side bolstering for the twistys