I stopped at a utility trailer repair shop yesterday and talked with the owner (who had been in the business ever since there was corn on a cob). He pointed out that one end of the pin was ever so slightly tapered, and said that I had to be sure that the pin was inserted tapered end first. He also said that I probably had not been hitting it hard enough with the biggest hammer I had. So today, with tapered end inserted, I started smacking the pin with as much force as the limited space permitted. Sure enough, it started going in, and after 20 or so whacks, it was fully inserted. Back in business!
Thanks to everyone for the suggestions.
