Jack - the tophat bushing, AKA flange bushing, is indeed taking the entire (~3lbs) load. Of course there is only a gravity load from the stone and pie, and thus no side load, to speak of, on the bushing. I kind of liked how the bushing drops into the steel cross member, and then expands w/ heat to snug up, so I stuck with it. Alternatively, you could just buy a couple of bronze washers to take the load (and save a dollar or two) then drill a 3/8" hole for the shaft through the cross member. I had a flange bushing, so that's what I used.
Also, everybody's pizza stone is a little different, but you might notice in the underside picture above that my stone has a thick spot in the center that is about 3" in diameter - a good fit for the pipe flange. For me, a larger flange wouldn't help because it would extend past the support area of the stone. The hole works great.
All - enough with the compliments. I've got all kinds of hours doing stupid grill tests to try various rotisserie designs for simplicity and reliability. Somewhere in a drawer, I have a degree which says I should be much smarter.