Thanks for your help! Turns out it was a taper pin, it just has a large hex bolt head on it - and a good thing, too. I don't know how I would have got the pin out otherwise. That sucker was in there tight! After a lot of careful wrenching I got it out, cleaned everything up, and am now in the process of struggling to get the pin all the way back in. Its halfway there - will start in on it again tonight.
Next question: When I go to refurbish my 29-4 - how do I get that pin out without damaging anything? It doesnt have anything to get ahold of, so I was thinking of using a rubber mallet and wooden dowel to try to tap it out from the back side. Is there any trick to getting the pin out on the 29s?
Incidentally, the reason I am taking the driving levers off is to clean decades of grime from the machines. I got them from a retired shoe man who had them sitting in his shed for 15 years at least. The good thing is, the thick greasy crud coating these machines has kept them safe from the Florida humidity - underneath it all they are in great shape.
Dave