I checked Rock Auto, and they picture the mount I have for an 88 Fiero like mine, so I ordered one. And for now, I cleaned off the surfaces of my broken one, put weatherstrip adhesive on it, and baked it in a 250-degree oven for a while. Then I put it back on the car.
On an 88, you have to loosen the parking brake cable to get to the nuts for this mount, because the cable goes through the front cradle cross-member (not like previous years, where the cable goes trough the rear cross member). So I'll leave the cable loose for now, to make putting the new one in easier.