When I put my aluminum one on my '82, I didn't drill at all. I cleaned out the holes and retapped them. The one in the back of the head needed to be drilled out, but there was now way to get a drill back there. If the holes aren't deep enough, just put washers on the bolts (that's what I did). I also put massive amounts of that sealer on the back of the head (where there was no bolt). Worked like a charm for me. You'll love the aluminum one.
1979 CJ5 project
"Life is an issue of mind over matter. Ya see, I don't mind, and well...you don't matter."
[B][COLOR=darkred]Red Jeep Club Member #2[/COLOR][/B]