BTW it's not a myth, and they are not steam holes. Unless you call a 7/16 size hole for steam. Ford and others recommend using the 351c head gaskets when that gasket is set on the block there are three large holes that need to be drilled along with one steam hole. You may get away with not drilling them but I didn't want to take that chance. As for head bolts they are 7/16 and can be purchased from ARP you will have to use the washer shims fom edelbrock or ARP to take up the difference from 7/16 to 1/2. By drilling the block and retaping you are strengthining the bolt but weakening the block. The block lugs for the bolts are not that big if doubt me look next time you have your car apart. I currently have a street boss 302 in my car using Aussi cleveland heads. I made this engine not for more power but to challange myself to see if I could do it. It runs great and has no cooling issues 110 yesterday in traffic.
http://www.darkhorseracing.net/clevor_head_mod.htm This is the web site that talks about the extra holes in the block.
