I finally got the steering wheel off by using a hammer and a screwdriver to break away the rubber from around the metal hub so I could use my 3 jaw puller. Even then it was stubborn, so I had to apply a considerable amount of torque to it until I heard a "pop" as the steering wheel came loose.
Since I'm gradually restoring the tractor, the steering wheel is eventually going to be replaced with a new one, so chipping away the rubber around the center, while a radical move, isn't a problem.