If you order a set of 14mm aluminum Maxx hex hubs, put them on in place of the stock 12mm. Then get a set of Imex diamond jumbo maxx wheels. You can then take set of Clod tires(not the stock tires; the rubber compound is too stiff), preferably made from a soft or medium soft compound, you can stretch the tires over the Imex wheels. That will allow Clod tires to directly bolt on to a GP.
However, the Imex wheels are of a larger diameter, then Clod wheels are. So you if you don't mind the large wheel/shorter tire sidewall look, then go with that.
I ran it on one of my GP's for a long time. It looks good, but I decided to swap on a set of Clod wheels, with TTR wideners.