Evan, one method I've used when making an adapter plate is to put a junk automatic transmission case into a band saw and cut it off just behind the bellhousing area, leaving the mounting flange for the pump in place. A centering disc the size of the pump housing can be made to very accurately position the remaining case to the crankshaft centerline. Then an extension of the crankshaft flange or the main bearing bore can be used as a center point for aligning the block and bellhousing accurately. Your idea of using wood instead of metal for the initial mockup is an excellent one! Metal lathes and mills cut wood just as accurately as they do steel or aluminum!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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