Heavy duty spindles for sure. I bot a set of these from northern tools :
http://www.northerntool.com/shop/tools/NTESearch?storeId=6970&N=0&Ntk=All&Ntt=go+kart+spindles&Nty=1&D=go+kart+spindles&Ntx=mode+matchallpartial&Dx=mode+matchallpartial
Im going to hack the ends off an old reinforced MTD front axle and weld them on for my wheelhorse - cool thing about aftermarket spindles is they dont have a drop ( for lowered tractors) BUT could adapted for lifted tractors with a reinforced offset welded to the axle for ground clearance.
Im going to build my own spindles for the wizard out of 3/4 grade 8 bolts.