302 casting on a set of 318 heads II

intake & head gaskets ordered ! parts store should have seals ! Wondering if I need double spring / valve springs ? only mild cam ! Not going to be racing this 273 but I want her to run well ! I have a LB340 intake I think correct . and a pair of 340 HP exhaust mani's. I'm thinking of a 500 cfm carb. still working it all out ! Much Mahalo for the help, C