I wouldn't go bigger than a E303 or something similar on a stock motor.
Usually you put in a cam after mods are done to round out and maximize the combo. The best specs for a N/A motor would need to be different than that of a nitrous
or forced induction motor.
Stay conservative if you gotta change it out. Personally, I'd would wait on the cam till you are ready to change the heads and intake as well.