You probably get to make wheels yourself, or have a wheel shop do it for you. Take the center out of a riveted wheel, cut it down in a lathe, and weld new hoops onto the center. I'm guessing either the hoops were welded much farther out than the normal 16" stuff so there would be clearance for the brake drum, or spacers were used between the drum and the wheels.
Are you recreating something like this?
