66" from the inside wall of the tailgate to the rear of the front drivers seat (seat fully to the rear)
42" interior height of hardtop to floor at rear cargo area
59" cargo area width from inside edge of "bedrail to bedrail"
61" interior hardtop width from window to window
43" cargo area width between rear fenders
36.5" cargo area width at factory subwoofer
47" width of factory rollbar at rear cargo area
36" height of factory rollbar from cargo floor.

Edit: These measurements taken on an '08 JK Unlimited X w/ hardtop and all factory panels, carpets, seats, etc in place.