Thanks for all the tips. I ended up cleaning and lubricating the shaft, and then the connector went on with just a little coaxing. No hammer required. And for those of you who are worried about it, I plan to put the mounting pins on the mower deck back the way I found them when I picked it up.
Once I'm done with the mower, I'll spend a little time on the turnbuckles.
Once I'm done with the mower, I'll spend a little time on the turnbuckles.