I put 01 seats in mine. I had to make an adapter/spacer to mount the 66 tracks to the seat bottoms. The seat bottoms are not flat and are different on drivers and passenger sides. I didn't have the 01 seat tracks so I don't know how they would work. Sorry I can't be more help. Dodgestang put Bullit seats in his fastback so you might want to search for him and ask him what he did. Might be more help than I am.
I concur with gp on this one. I thought about working on getting all the power option to work, but the seat was just too high in the car. I would have had to lower the seat pans which was something I didn't really feel like doing.
I unbolted the 65 tracks from the 65 buckets, fabed up some spacers and bolted the 65 tracks to the bottom of the 01 seats.
Even with this application in the stock location the seat was just a little too far forward and a smidge too high for my tatse.
I left the passenger adjustable and then on the driver side I took apart the sliders and just bolted the part with the studs to hold the seat in down. I also drilled 4 new holes in the bottom of the seat (originally I only drilled 2 and used 2 of the factory holes) and moved the mount as far forward as it was physically possible to put a nut on a bolt to tighten it up...then dropped it back down in the stock bolt in location. This moved the seat back about an 1 and down about a 1/2 this combined difference made it a perfect fit for me...and about 90% of the population. It just doesn't slide forward...so rear seat passengers need to enter and exit from the passenger side only. Not that I ever carry anyone in the back...it still tips forward so you can get to stuff in the back easily enough.
Guess what? I'm in exactly the same boat as you. Just finsihed painting my 65 fastback and ran across brand new, charcola grey 03 GT leather seats. I have got to find a way to make the driver's power side work!
I did some experimenting. The plug on the bottom of the driver's seat is simply for a set of pins for a battery/ignition hot power and a ground. Seat moves all over the floor with a jumper connected. So power isn't a problem.
The passenger seat is just a slider, so I am going to hook my old seat's slider to it. (Hint new holes will need to be drilled. Drill them at the very front of the seat. This is counter intuitive, but will allow you to slide the seat further back!) Once I get the passenger seat in, this will provide me a baseline for the hieght the driver's seat needs to be.
I think cutting the drivers seat pan is going to be required, but they are cheap and fairly easy to replace. What would be realy really helpful, is a picture of an 03 mustang's floor pan! I'm going to go to the modular section and ask the folks there for help!
I'll forward any info I get. Please keep me informed of your progress!