[Andy]

This exact same thing happened to me. The part that fell out goes between the turn signal stalk and the number 77 in the diagram. I had the same problem with the over sized pin too, sticking out just a little too much. I did not feel competent to tear down the steering column (which is required to get the plastic piece back in) so wound up taking it to my local Corvette specialist. He said the one over sized pin really wasn't going to fix my problem either. Ultimately, he wound up replacing both parts of the hub with NOS (He had a source. If I can find it I'll post it).

I found the source;

Steering Column Services
889 Molinaro Ct
Ivins, UT 84738

I don't have the phone number though.