well if you're going to go 4bbl on it, i'd reccomend just swapping the cam and get a edelbrock cam, lifter, rocker, pushrod, intake and carb package. the cam gear shouldn't be plastic it should be nice hard iron possibly even nodular iron. the compression drop ford did was chamber size on the heads. a 70 302 should still have around 8.5:1 compression ration..... if you want some heads with a little better flow but still keep the compression down, get some AFR 165s with larger chambers, go for like the 64cc chamber or so... i personally run 58cc heads, but i like compression...