My 12yo son has a 04 KX-85, my 13yo son has a 02 kx-100. The 12yo races mx locally and is on the verge of getting to tall for the 85, but fits the 100 fairly well. He is not ready to move up to the "supermini" class which is the required class for the 100 in AMA races. Is there a "big wheel" kit available for the 85s or what can we do less putting the 85 motor in a 100 chasis? TIA