I went down the the machine shop, and the bottom end guy and I looked at the mains. They are all the same size in my block.
I am pretty sure these are ARP studs, as the block was at some point, a CMRE product... That, and I dont know where else they would possible come from.
When I took the block down, there was just enough threads left at the top to get a nut started on there for the oil pickup. The nut definately was not all the way on, but I'd imagine 2-3 threads would be OK.
He is going to figure something out for me, because I am putting a Morana stud girdle/windage tray on mine.
On the factory shortblock, there is a bolt with a small stud protruding for the oil pickup.
Hope this helps...