Duels on the cubs were an option from IH as a means to better stability and floatation on golf course sand traps, to mowing on hills. They also provide better traction and reduce the foot print left on lawns to keep them in better shape. Duel wheel extensions can be found at xtrememotorworks.com and are the over all best bang for your buck in my opinion when it comes to the parts they offer. There are other ways to make your duels but ill leave that for some of the other guys to chime in.
Hope this helps!