Seat belt hole on new floor board

the factory nut on this 67 barracuda fastback part of the inner rocker? or do i put one in
The bolt points to the outside of the car there is a captive nut welded inside the rocker. You can not get to the back side of the nut.

You should be able to take the kickplates off and pull back the carpet to see the hole and test fit the bolt.