On my agway im running 4 rear tires ( 8" rims) - its taken a back burner to other projects tho- i do plan on doing more mods and getting it running - already swapped pulleys , not for tons of speed- just a lil bit more . Heres the agway:
To run the rears on the front, i had to weld bolts on the spindles- eventually im upgrading the front axle/spindles.
You could custom made new hubs for like golf kart/atv rims - i bot a set of golf kart wheels for $40 from a flea market. For mine i bot a set of bering front hubs and keyed back hubs from northern tools.
For a basic upgrade you could just source a set of ATV tires and put em on your stock rims.