Do you mean ARP studs Pete? Every SB I've done using ARP studs had major interference issues with the pump not allowing it to pull up tight. I usually spot face the main cap .050" on the side where the stud hits, trim the stud down just as short as possible, use a thinner nut and washer (grade 8 of course) and grind a little on the oil pump then it clears.
As for a couple other things mentioned
1. the plugs behind the cam plate. I've torn down engines without them that had no oil pressure issues. I also once had a fresh 360 with low oil pressure and when I took it apart I found those plugs missing and thought aha! I found the problem. Put them in and no change at all. Found the lifter bores worn badly on it causing the low oil pressure. Even though I've seen those plugs make no diff. I still install them just cause.
2. The head gaskets CAN NOT be installed backwards. Anybody that thinks they can must have a block with no dowel pins. Those dowel pins are offset to prevent installing the gaskets backwards. I attached a pic showing them being offset
3. Oil feed to the rocker shafts is only a few degrees of rotation so the cam has to aligned nearly perfect for the oil supply holes to feed the rocker shafts so the only way you will have oil pressure to them is when the engine is in exactly the right spot of rotation and it's different for both sides.
Check out the last picture I attached showing a commonly missed oil galley pipe plug that will cause very low oil pressure if left out. I think you said you checked it so sorry to be repetitive. Just want to make sure.