How do you suppress caliper on a 93 Lumina enough to fit pads between rotor and shoe-vehicle has a 4 prong screw in piston vsa slide in but won't seem to go in any farther?

You can get a caliper piston compressor tool at most autoparts supply stores. Some even loan them for free if you buy your parts from them. Another option I've used is a thin piece of plywood [to protect the face of the piston] combined with a "C" clamp to press the piston back into the caliper. Usually, once the piston is fully returned into the caliper, the clamp and plywood can be removed without the piston moving back out. If it does, then recompress it, and just slightly "crack" open the bleeder screw [only momentarily to relieve the hydraulic pressure]. Then the piston should remain fully inside the caliper after the clamping pressure is removed. Good luck.