Well it seemed like a lot of torque when I was sitting on the end of that wrench last night! I think I got them more than tight enough, and also used blue locktite for some insurance and paint-striped the bolt/nut as alancamby suggested. Will periodically check everything whenever I tow, of course.
I thought about firing up my impact gun, but it's a 1/2" unit and all of the 1-7/8" sockets I found were for 3/4".
Interestingly, the 2" ball snugged to the point where I only needed to wrench on the nut to tighten it all the way home. The 2-5/16" ball kept wanting to spin so I had to wedge a pipe wrench between the flats on the ball base and drawbar to snug it up.