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Studebaker / Avanti Crankshaft flange/pulley dimensions
Dave Livesay, SDC Forum - Nov 2008

here is a sketch of the pulley bolt pattern from the pulley interface side NOT THE DAMPER pattern. The damper pattern is the same but with the 65 and 55 degree measurements reversed.

I measured one of the R3 pulleys. This should be accurate. If you have X,Y corrdinates you can just use some Trig to see if your hole pattern matches. The only possible error would be the one offset hole could be off by 1 degree, but I don't think it is. With the clearance hole size it should be ok in any case. Since you have a pulley I would suggest that you make an adapter that pilots on the damper and the pulley. The below sketch shows the idea. I WOULD NOT attempt to use the bolt pattern to center to pulley to the damper.

Just machine a pilot hole on your pulley and then make the adapter to fit.

This is the crankshaft Flywheel flange