I looked, not sure if the big cubes test automatically holds true to the 318, but worth considering. I know I can gain both ways, I just want the biggest gain. Leaning towards the 308 heads. I know 8.5 compression will run real nice on todays gas and perform very well. Last time I used 360 heads on a 318, we milled them .045 and used a fel pro head gaskets, but they were late 70's heads.