it's 1/4" socket head pipe plug at the end of the lifter galley on the driver side. it's in front of the intermediate shaft. probably can't see it but with the intermediate shaft out you should be able to stick a finger back in there and fell for the plug. a test would be to drive the oil pump and see if any oil comes out the back of that galley. any oil comes out and the plug is missing, common goof up. in fact your oil pressure issues are nearly identical to what i experienced with a 360 without the plug.