Thanks for the input boys. Carl, I think we have met. If you are the guy from SoDak, we met at the AMCA run in Steamboat Springs 2000. I was riding the red and white flathead and spoke to you of mutual aquaintances in NoDak, where I'm from, originally. Anyway, when reassembling last night (with new studs), we discovered that when torqued down there was a slight binding of the shaft. Closer inspection revealed a shiney spot on the top half of the rocker block "bearing" surface, indicating possible binding during operation(?). A light pass on the honing machine resulted in no shaft binding upon assembly. My thought is that a slight bind in the rocker shaft was accentuated during operation because of the difference in the heat expansion coefficient between the brass rocker block and the steel shaft. The shaft binding (although not completely frozen) created excessive pressure on the valve train and the weakest stud failed first at its base and the other three followed by shearing at the nuts.