4.3 L misses at 4000 rpm
 

I just acquired a mariah junalee with a 4.3 L engine. The starter blots were sheered off, and the engine had to be removed to repair. when it was reinstalled it had no oil presure and the oil pump had to be primed. It then started but around 4000 rpm it was missing. I have to add that the original engine overheated and the block was replaced.could the manifolds been damaged when this happened and possibly been the cause for the bolts to sheer ?