On the SBM..... the correct bolt (the long bolt) tapers to .420" in the area in its midsection IIRC, where it is in the middle of the head (vertically) to let oil around and through the bolt hole in the head. The Edelbrocks RPM LA heads have the same bolt hole diameter as the stock heads here, so the long bolt goes in there just like for the stock heads. Use of ARP studs puts a stud that is .500" up through that hole in the head, so it makes that area fairly restricted but does not shut the oil flow off entirely. The flow area where the rocker shaft meets the head pedestal is the smallest flow area and the stud in the head makes that bolt hole area small too.
