Auto-conversion adapter plate

Well, I sold my big, custom-made bellhousing to another builder that
wanted to get that radial look out of a rotary engine. That 21 pound
chunk of aluminum just wasn't going to go nicely into the front of my
Delta, so it's all for the best.

But now I'm in somewhat of a lurch. I need to build an adapter plate to
match my PSRU up to my engine. The Mazda 13B rotary is nice in that the
engine comes apart like loaf bread (after you remove the 17 large
tension bolts), so I have a nice template to make the housing from so
that I could just match drill the bolt holes. What I can't figure out
is how get the alignment correct. I can drill a hole in a plate of
aluminum for the PSRU, but how can I then hold that hole concentric to
the engine's output shaft while I do the match drilling? Alignment is
critical, as any offset will vibrate my teeth out and will eventually
destroy the coupling.

Any ideas would be greatly appreciated, as I think I'm going to be down
to spending money at the machine shop for this one.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."