Top end not getting oil up from lifters
You will have to pull the timing chain cover and take the galley plugs out. Also there are three on the back of the block. You are checking for thrash, pieces of RTV, etc. Blow them out with air hose. The plugs are 1/4" pipe plugs. I would start on the back first if you find some thrash or silicone behind the plugs I would hook up the drill and see if you have oil flowto the lifters. Never use teflon tape on the threads use the teflon paste. This includes fittings from your guages too.