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I have something to work with now. I see Eckler's use to sell an adapter kit but it is marked as discontinued now. I think I can get there from here now with the article you posted.
All of the C2/C3 steering wheels (except 1976) attached to a die cast hub with six screws. I would think that most aftermarket steering wheels were designed to bolt right onto the production hub with six screws as well. So unless the aftermarket steering wheels were much different, I would think that any "adapter hubs" would be very similar if not identical to the Corvette hub.
Unfortunately, I see that the original Corvette hub 3949110 is no longer available through GM dealers. I also see that the one listed by Zip Products SC-413 says to CALL (not a good sign). I thought that there was a hub available from some sources but I don't seem to find it right now.