front bucket seats on '68 Barracuda

The studs through the floor are swedged into the tracks. You may not need longer ( depending on how much shim you need ). If you do need longer hardware, you'll remove the seat, hammer those studs out of the tracks, replace with hex heads, struggle and fish under the seat with a end wrench at reinstall, etc... or make a carriage bolt with similar square shoulder stay in the track ( tack weld it? ).
Be cautious when moving the seats back into the car. Those studs can feck up a door panel quick. Any way you go about it, the more the 2 tracks are skewed from parallel the more bind/difficultly in slide forward and back. Good luck with it.