I bought a kit for my rim clamp tire machine that lets me mount 6-12" tires on ANY wheel. Those basdards go on the rims whether they like it or not. As far as airing them up, forget tubeless and toss a tube in there. Be sure to file all the ridges, weld flash, and sharp edges off the inner parts of the rim. Wheels intended to have tubeless tires don't get the extra finishing needed to prevent tube punctures by the unfinished metal crap left on the inside surface.
For really small gauge and mower deck wheels, I recommend solid or foam filled. No more Vise-Grip mounting episodes !