This URL: should help you out..go to the interior section.. I just had a pair of 1985 1/2 SVO seats reupholstered and I installed with old seat rails from orginal Mustang, " just drilled and tapped two more holes on the seat frame for the new rails. good luck
The 2000 seats are different than the 85-9? seats. There was a thread on here not too long ago about late model seats. Do a search for it. That thread will answer all your questions,
I have 2001 seats in my 65 mustang. The easy way to make them work is to take off the new tracks and replace them with the tracks off the 66. You will need to use spacers to make the old tracks work, because the bottom of the seats on the newer seats are not flat (front to back) like the older ones are.
I'm sure there is a way to keep the new tracks and power on the new seats, but it would not be easy. In oreder to keep the new tracks on the new seats you would need to lower the seat pan to make head and leg room. I'm 5'10 200 Lbs. the new seat with no mods other than changing the tracks are a comfortable fit. Hope this helps.