Ive heard of & seen the passenger side oil galley plug be left out by builders that dont know pontiacs very well. I bought a car a few years ago that had a fresh build high dollar 455/474 stroker in it, the shop & owner couldnt figure out why it ran so rough, would misfire & sputter & backfire... gauge showed good oil pressure. he was selling the car due to a divorce but tried everything & numerous "mechanics" to get it running right then finally threw in the towel.
Got it home, did some basic testing for firing order, timing etc, everything was ok, so i finally pulled the valve covers to inspect rockers etc... started it up & instantly saw the passenger side rockers barely moving, knew right away that it was wiped cam lobes or that oil galley plug was left out. Cam looked good visually so pulled the dist & sure enough the plug wasnt there... was able to carefully install it through the dist hole, fired it up & it ran great! I pulled the new E-heads heads & other external parts & sold the short block to a guy that kept in touch & sent videos with his new parts on it, said it ran great. I kept all the parts for a new stroker build using a 400 block & forged butler rotating kit. The 455 had a cast stroker crank & KD hyper-U pistons that i didnt want to use for my build.
That rear oil plug can cause running problems but the engines oil PSI should be good without it, just low psi on the pass side lifters.
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