If it's for your 87, the GM factory hartop will not fit without an adapter kit. The hardtop (RPO CC2) came out in 1989 and those cars had a flat mounting plate on the inside of the B-pillar an just below the plastic corner trim piece. There were two threaded holes on the side of the plate and a small tab at 90 degrees to the plate at the bottom.
On the later cars, there is a captive bolt in the windshield pillar that holds the front of the hardtop top in place. The rear decklid latches should have a nut welded to the bottom of the assembly to take the captive bolt in the rear locator pins on the hardtop. Not sure if your 87 would have them but the retrofit kit includes the assembly.
I have scanned pics of the hardtop install instructions that came with the factory top and I 'll send those to you. But until you get the adapter kit, the top won't attach to the 87