I may have a problem...again. There is supposed to be a bolt plugging the oil galley at the rear of the cylinder head. My 1960 TR3a.. It's not there. Can anyone tell me the size of the bolt/plug. I was told it was 5/16-24. It's not.. 5/16 falls in and I can't get a 3/8-24 started. Help please. I seriously don't want to pull the head. There is only about 1 inch between the head and the firewall. Could it be Whitworth sizing? TIA