[e015475]

This should be obvious, but did you plastigage the rods and mains and make sure you're bearing clearances were correct? (I've screwed this up once - I assembled a motor that I'd had the crank turned undersize without checking the rod and main clearance because the machinist said he'd done it, and it had the wrong bearings - oil pressure at start, but noisy lifters as soon as it warmed up)

Best practice is to have the machine shop measure the installed bearing's diameter with a dial bore and the journal with a micrometer to arrive at a bearing clearance, then double check with plastigage when you assemble. Do you have a build sheet from the machinist?

Did you replace the oil pump, preferably with the higher flow one, during the rebuild? Did you use a new factory o-ring on the pickup? Did you thoroughly clean the screen on the pickup end?

The barbell's purpose is to divert oil through the filter after it leaves the pump so as not to have unfiltered oil going to the bearings and lifters. Leaving it out would let unfiltered oil into the bearings/lifters and cause failure down the road, but I'd think oil pressure would be incrementally higher without it since there's no pressure drop across the filter.