7" wheels are what is recommended for 9.00x20 tires. And the 3 piece wheel you have is the safest tube type wheel ever made. 22.5 tubeless wheels will bolt, but most of the 22.5 wheels available today are 8.25 wide. Quite often this causes problems with tie rod end clearance. 7.50 x 20 were common years ago, but I think they are getting hard to find. A 295/75R22.5 on a 8.25 x 20 wheel would be ideal if it will clear your tie rod ends. Spoke wheels are still common on trucks that see a lot of abuse like garbage trucks and on container chassis because the wheels don't get stolen because they can't trade them for drugs like a tire mounted on an Alcoa. If you are going to use the truck for parades and such, the tube type tires will be just fine. If you plan on driving highway speeds tubeless would be worth considering.
