1993 GMC C1500 low oil pressure and valve tap

Sounds like you may have hurt the engine. Overheating can push a high mileage engine over the edge pretty easily. My 4.3 went 205k got it hot and it was never the same. Sometimes if theby-pass spring breaks in theoil pump it can make thevalves noisy due to lack of pressure, but it can still oil the bottom end, no promises, but that may be it. The misfire is most likely a cracked head or blown head gasket, the head castings on those are weak and tend to crack