The 88 had a completely redesigned suspension and braking system. The 88 cradle can be installed in the earlier cars with some adapters to relocate the struts, but coil-overs will be required. The 88 front suspension is, for all practical matters, not able to be swapped into the earler cars.
(One guy on this Forum has done it, but it involved a lot of cutting and fabrication.)
Interior pieces are interchangeable.
IMHO, if your GT is trashed, the easiest option would be to swap your V-6 into the 88. Will require a different front engine mount, maybe a different exhaust Y-pipe, and not much else. Use your V-6 harness and computer.
All of the GT bodywork, including ground effects and fascias, can be installed on the 88.
Several folks on this forum have done similar swaps (engine and/or body), with great success. You can search for info. Link is at the top of the page.
Welcome to the Forum.
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Raydar - aka Steve
Black 88 Formula.
Red 88 Duke coupe. "The Project"
88 Formula parts car. "The Donor"