Oil pressure concern

Did your engine builder run the engine on a test stand or dyno before it was delivered to you? If not, was it full of oil with the pump primed?? If not, what did you do before starting it up? Small block pump can suck air if the pump is not fully seated on the rear main cap. There is also a oil gallery plug inside the cam valley facing backwards next to the intermediate shaft bushing that must be installed tightly. Ask him also about the little welsh plug by the rear main cap. There is a certain depth that it must be driven in to. Did it take long for the engine to start up? You should have better idle pressure than what you state. That would be low even in a clearanced race engine, so there might be one of the issues I mentioned, or a bearing problem. Good luck.