There are major differences and there are small differences. Even the engines are different, so your best bet would be to look for a parts car just like yours.
Front cradle and everything attached to it. Rear cradle and suspension (except struts) Entire braking system Under-car coolant tubes Spaceframe is different in regards to front cradle mounting area Alternator Exhaust crossover, downpipe No provisions for trunk blower Gen 2 headlights and controller Oil pressure gage in aux gage pod Beechwood (brown) interior pieces Dot matrix cluster trims
Some more not so obvious items: Flywheel or flexplate Crankshaft Fuel injector harness Y pipe Down pipe to include everything from the flange to the exhaust tip. Rear sway bar Front sway bar? Front motor mount 87 and 88 has an evap canister in the right rear fenderwell near the battery Fuel tank is larger
Some V6 88s have a different (square) connector on the FI harness. Some have the flat connector that the earlier V6 cars had. All of the flat connector harnesses are interchangeable.
some more: 88 had a unique ground wire attached to the rear deck lid b/c the panel is inside the lid vs. bolted to it. Different off-set for the front rims. (unique color) Seat material/pattern is unique to 88.