Is the distributor housing supposed to be sealed? on 2001 Chevrolet Blazer

When applying pressure to distributor housing the blazer idles ad accelertetes more normally, we just had the head gasket changed but the distributor housing seems to be loose and the RPM gauge is flutering and oil pressure is lower than normal and we found a bolt siting on windsheild deck.

Asked by for the 2001 Chevrolet Blazer
If bolt is for dist holddown then the dist is moving up and down in bore and causing timing problems and maybe the oil pump drive is skipping. Have inspected at the shop that did work or if you did it then back track your reassembly steps.