whats the casting number on the intake manifold? i really don't know to much about 366's, but i'm pretty sure that they did not come factory with square bore high rise intakes, but i be wrong. I'm assuming on the year (1978) of the heads that they are very similar to 049 and 781"s, which are very good heads! i would put 2.19 and 1.88 valves in because your 500 cube mill has big bores and heads would really pick up the flow. a 500 cube motor with large oval ports would make very good power especially the torque! 1992 john ligenfelter put ported 781's large oval ports on a 502 BBC and made 650 horses, just in case your wondering. I would hang on to that intake, does the intake have any casting such as HI PER(hi performance) or PASS (passenger)?