Ok I tried to find the write up that I followed when I did this in my second gen camaro. But sadly google has failed me and that was like 5 years ago. But I'm GUESSING the theory would be the same. If you had bucket seats in your 66, and don't mind giving up the seat base power function (the seat back will still have power) then you can take the factory bucket seat tracks, weld 1" square tubing to all 4 corners and then weld those to the Late model seat base, it should fit fine. The write up can obviously explain it better so I'll keep trying to find it.