The slants used a reduced diameter shank on the last head bolt on the rear passenger side of the car to feed oil to the top end. If a normal head bolt is installed in that hole there is no oil being fed to the top end. Food for thought.
Nope. All head bolts are the same. Some heads used a reduced diameter rear rocker shaft bolt, but since the threads are different, you cannot install the incorrect bolt.
If the engine was a complete rebuild (meaning hot tank of block and heads), the most likely cause of no oil to the rockers would be, either the rocker shaft itself is plugged up, or the rear cam bearing was not installed properly.
The first thing to do, is determine if it is low engine oil pressure, or just low/no oil to the valve train.