you'll need the lights, trunk lid and rear bumper for a clean swap...you'll need to redrill holes in rear panel for the screws to go through and shave some off of the back of the lights for it to sit properly...or you can swap the rear panel as well--will require welding.

If you don't swap the rear bumper, you'll be left with about a one inch gap, as the 90-91 lights are that much shorter than the 88-89s