Hmm, interior stuff.... That will be different. Im not sure on what will not work. But, it would make sense that the headliner, rear package tray, rear side mouldings and possibly the rear seat will not cross over. The front seats dash and everything else should work. Will you be able to have both cars side by side?
Rear package tray (the plastic one underneath) swaps, as does the rear seat.
The rear package tray cover (what you see through the rear window), does not.
I THINK the headliner swaps also, since the upper end of the rear window is in the same position, and the rear sails cover the B pillar difference.
The outside mouldings will swap - matter of fact, the 92 and 93 LX TBirds used the same moulding the 1991 XR7 did (!!)
All the underbody parts swap just fine.
All drive train parts swap fine.
All interior parts save the sail panels should swap just fine.
Rear window, trunk lid, etc. are different.
Rear tail lights are different.
Front fenders and doors are the same.
The differences in the upholstery are that certain options were only one way or the other, and the Tbird will tend to have a TBird in it, the Cougar, not *grins* But they do swap.
RwP