Thanks, all! I'm thinking of making a jig using hardened drill guide bushings in a bolt-on steel plate to take the guesswork out of drilling a head. I believe the head bolt holes adjacent to each pair of holes are similarly positioned, so the jig would only need to be 2-3 inches wide or so, and use head bolt holes for attachment.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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