I think any seat will pretty much work. The question is what has to be done to make it work. I have the exact same, Recaro style buckets from an '86 or '87 GT that TheChevyEater has on the following page: http://forums.stangnet.com/showthread.php?t=513328&page=39 (just scroll until you see them).
I put these seats in my car in @ 1990. Although I don't recommend it knowing what the good folks at :SNSign: have taught me since that time, I completely removed the seat platforms when I replaced the floorpans and installed the seats. However, I'm not concerned with the structural integrity of the car as I welded two heavy gauge angled steel braces to the rockers and the transmission tunnel to mount the seats from on each side, and I have subframe connectors.
Not to hijack, but does anyone know if replacement seat foam is offered for these seats that would give you more agressive bolstering? I love the look of the seats with the open halo style headrests, but my seat foam is worn at this point, and I would like more aggressive bolstering ala Scat Pro-Car seats.
67GTA- First I would recommend doing a search here there use to be some good posts on the topic. They can be used in your car, however, you will need a little ingenuity. The 01-04 seat tracks were designed for an uneven or curved floor. When mounting them you'll need to build-up one end of the tracks. Some have fabbed a riser, others used washers. Second, the holes are in diffferent positions so you'll need to drill. BTW, should you be interested I have a set of Dark Charcoal leather seats out of a 2002 GT with only 13,000 miles on them. They were removed, treated with lexol and placed in storage about 10 months ago.
If you want a sportier look than the later model Mustang seats, try these. They are Recaro seats from a Honda S2000. The dimensions of the seat fit perfectly into 65-66 Mustangs interior (haven't tried them in 67-70). Just remove the seat tracks from your original seats and redrill them into the new seats (used to mod recaro tracks but was told here to redrill seats with oem tracks).
IMO, I like the headrest net and they look modern but not too overdone, plus they are in high quality leather. They are soo comfy, finally find a way to attach the lapbelt so that you can also use the modern safety belts in your car.