I have the center sections of a pair of space-saver wheels on one end of my rotisserie on some junk front stub axle carriers from a front-wheel drive car. I just drilled out where the rim was welded. The centers of these are pretty heavy steel and look like extra large casters. They roll nicely on concrete but not well at all on gravel. I'll have to swap them for tires *and* wheels, as you suggest, as each end of the rotisserie clears the doorway.
Haven't added any to the other end yet -- haven't decided whether I should use front spindles so they can steer or rear ones for fixed. Thought about just temporarily attaching the rear-end from the Olds to the rotisserie, cobbling a starter motor and pulleys to it, and letting it push itself outside and back. Hey, that rear-end is useless until I get the frame out of the rotisserie, anyway.