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.
The rear seat cushion you push towards the back a little then pull up on the front edge. The seat backs have two bolts per back on the bottom which are hidden by the seat cushion. After removing the bolts tilt the bottom of the back out and slide the back downward to clear the hook. Oops!!! You have to remove the armrests on the quarters first before you even pull up the cushion. Just two bolts per. Good Luck!!!