The oil feed line to the rockers from the centre cam bearing or upper block surface may be blocked by your head gasket or may not be drilled in the head if you have changed heads. Did you put the thin head bolt in the centre oil feed hole?

I think would think the only thing to do would be drop the rocker arms of, crank up oil pressure and check for flow to the top of the head?. If not then take the head off and check for flow to the top of the block.

There are two different oil feed systems to the rockers. One through a restrictive drilling in the block connected to the main oil gallery, or two from the centre cam bearing around a thinner head bolt up to a diversion hole in the head that directs the oil to the rocker shaft.

Good luck