The head gaskets being on backwards will not inhibit oil flow to the rocker arms. By design, the head gaskets have two oil holes in them so the gaskets will work on either side of the block. Here’s a couple of head gasket pictures.
If you have a cross-drilled camshaft rather than one that’s grooved, that particular camshaft may have be turned so that the oil can pump through the cam to the top. Slowly turning the engine over while pressurizing the oil system will find one side getting oil and then the other in a back and forth sequence with the cross-drilled camshafts.
You might trying blowing air down the oil galley hole from at the hole exposed when the rocker pedestal is off and see if that blows the oil galley in the block clear. Otherwise, you’re looking at an oiling problem around the cam bearing area. Back in the Seventies, it was customary to pump white or lithium grease into the hole to unblock the oil passageway in the block. A flat plate with a zerk fitting would be bolted to the head with the rockers off and grease pumped into the hole.

Lorena, Texas (South of Waco)