Jon,
I have a 11 bolt head and it was installed by drilling and tapping the extra
holes in the block. As far as I know, that is not necessary, but preferable.
If you are doing a total engine referb, it would be good to do it. Be aware
that your valve cover and gasket will have to be hogged out to accomodate the
stud nuts which will conflict. It is best to use those sexy ARP nuts for
that (see pics on my site - below). If you do not use the extra holes, you
may want to fill them somehow so that crud does not collect.
John Carey
http://ourworld.cs.com/JCareyPage/JCareyPage.htm
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