In the absence of an adapter plate....

Without being able to see what you have on a bench, and without being able to take measurements.......
I would take the crank out of a blown engine of the same type you have, put it in a lath and cut off a piece, saving the last 1/4 inch
of the crank for my adapter plate.

I would buy another pilot bushing and with a lath I would cut off 1/4 inch.

Next remove the stock pilot bushing, place the 1/4 inch short bushing in the crank hole First
and the longer stock pilot bushing would go in last to get the maximum support for the pilot shaft.

I would use graded bolts 1/4 inch longer than stock.... maybe from ARP...through the flywheel...then through my adapter plate holes, (remember it's made from the last 1/4 inch of an engine crank), and then into the crankshaft end.

An alternative is to get a caged roller bearing and substitute it for the outermost pilot bushing, but that requires some research.

This solves the adapter plate question because you just made an adapter plate,
and coming from a crank of your same engine type..... the bolt pattern, diameter of holes and outer size of the crank
should all be the same.
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BTW, this does not require a drawing and does not require making something from aluminum.