You know..... I just re-read your first post - I think I misunderstood your question about the bell bolts. The size I mentioned are what I think attaches the bell to the block. It looks like you were meaning to ask about the bolts that attach the starter to the bell, correct? I think those are 3/8-16? A quick way to measure for the proper diameter is to measure the clearance hole. If you have calipers handy, they will be the next nominal size down from what you measure. Industry standard for clearance holes is 2 drill sizes over nominal, so a 3/8 (.375) bolt will take a 13/32 (.406) clearance hole.