I have the kit to convert / swap the SM wheels to true dirt wheels.
This kit was $800 from the dealers if you could get them.
see attached jpg
Comes with:
18" rear wheel/rotor
21" front wheel/rotor
different speed-o gear for 21" hoop
different caliper hanger
extended lenght side stand
tires are pretty shot about 5k hi-way miles.
shipping without tires should help reduce cost.
$350 plus true shipping costs.
Note: It took me about 1 1/2 hr to do a swap the first time.. then 1 hr.