Well if they are like the Mustangs yes there is a plug in the sub floor underneath. These plugs are rubber so they might be gone. But if they are there you just pry them out with a screwdriver and that should reveal the seat track bolts above. The Mustang nuts were 1/2". There will be 4 nuts that hold the seats down. Again I'm not certain of the Tbirds but they might be the same. Worth a look anyway. I'm sure someone will chime in with the correct info.