the california model has the epa carb and exaust , take off throw away. get the governor out , billit rod and flywheel , you wont notice any difference. i have both models . currently using the ca block with the rtb-02 head , it has bigger valves than the rtc 6 , the rtb-02 comes stock with 10.5lbs. valve springs , upgraded retainers and keepers {but they suck} get billit keepers , the aluminum ones they use on racecars. if you build a rtc 6 and a rtb 02 with the same parts , the rbt-02 will out perform the rtc 6 , bigger intake and exaust valves.