you can get the 4mm cubs in either 65mm or 68mm(big bore). most people seem to go with the big bore whcih puts your displacement right at 421cc. you can either run a big bore pipe or something like a small bore cpi, shearer or rockets. for dragging this setup will kick some ass. wide open roads i think youll be fine as well. as forthe trails i dont think itll be all that great there, but you said you dont ride them that much. the cubs were designedto use all stock parts. so if u have shit thatll fit stock cylinders, itll fit the cubs.
call jeff @ FAST racing. he should be able to get you cubs..1-785-364-5325