From what I've seen (depending on the vintage), Williams dummy trucks may have some of the gears required, but not all (usually missing one or more of the spur gears that pass power to the other axle). A can motor (with the Williams mount) will bolt right on top. There has been a fellow at York who has a bunch of older Williams parts, including wheels and gears. Have not seen motors, but he has the mounts and you can mate up a number of can motors to it. Just have to find that worm gear!
I have bought complete power trucks from this guy (I think his first name is Frank, Orange Hall, near the front entrance, his table is right on the end). Parts in cigar boxes, you have to dig a little, but ask him what he has - most likely some stuff is back at the ranch.
