Kevin, I just finished a cab off resto, and if I were to do again, I would look further into the rotisserie. In fact, I think a good pivot point would be about the top of the engine recess in the cowl, to make it less top or bottom heavy.
Actually, my plan is not to rotate it about the front to back centerline, but crossways, mounting the cab using door hinge and strike attachments. I realize it will make getting to the interior a bit restricted, but I think I can deal with that. I figured the geometric center of the cab using the cab dimension figure from the FAM (Sheet 1.07). The height of that point is a bit below the top hinge, corresponding with your recommendation. My cab floor is where most of the action will be and there's not enough meat left there to support it from there, like a "standard" rotisserie would.
