Dont know where to buy the wheels at the best price, but on the yz you only need the wheels.The swingarm is only 12-15 mm longer on the big wheel version.The wheel will fit,but you wont have as much room for adjusting the chain as normal,no big deal.When you buy a big wheel bike,the fork and shock springs are stiffer,so a soft spring for the big wheel version will be the spring thats normally on a small wheel version.This is off course only neccescary,if the rider is heavier.The wheels on the rm 80/85 are the same,the rear brake disc is also identical,so you shouldnt have too much trouble finding a set of wheels.