318 top end build

302 heads will only give you about a .5 bump in compression ratio and flow the same, really no gain in power, the only advantage since your not building a quench engine is closed chambers would need to be milled about .020" less to get get the same CR than open chamber. If you can get a low mileage set dirt cheap and mill and port them might be worth the swap but if you have to put too much into them, EQ's would be better choice. I'd go stock longblock high lift 262ish cam, headers and 4bbl.