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.

 

Starter motor solution for a flywheel that was moved back 1/4 inch.
One solution comes from post 16 above:
"We left the flywheel in the stock position,we left the ear on the adapter plate to align the starter.and we machined a new outer shell to hold the pilot bearing to make up the .125". We removed the factory block shim so the new output shaft location is .125" further backward closer to the rear. We found that the driveshaft slip yolk had more than enough room to accommodate the new location."
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Without seeing your stuff on the bench where things can be measured......

If a starter is forward of the flywheel....
Another solution to move a starter motor back 1/4 inch to engage the flywheel,
is to machine 1/4 inch off the starter mounting ears, so the starter goes into the bellhousing hole 1/4 inch further
and keeps the starter-to-flywheel distance the same as before you started.

Plan B is to buy a new high performance starter and do whatever is needed to space the starter gear on the flywheel teeth properly.

 

Now tell us, what is the reason that the pilot shaft ends up 1/4 inch further back than stock?

Help us get smarter. Thanks.

 

James, this is an old thread but do you still have the CAD drawing of the adapter plate?