The bad thing is that if it's really restricted that much, he'll have to pull the heads to pull the restrictors out. In his first initial posts, he mentioned that the restrictors were in the deck. Some builders drill and tap that passage in the deck of the block, while others just restrict the passage under the rocker stud itself.
I second(third, fourth?) the vote to run the engine with a valve cover off. But since it only happens when hot, I'm leaning towards excess clearance somewhere.
As for the
oil pressure issue, I've had FE's that I've built run about 25-28 lbs while idling with a HV pump. It's not an issue as long as they build
oil pressure when the engine starts gaining revs.