Plus heads, a 408 is gonna have a hard time making a lot more power than a stock head 318 if you also slap stock 318 heads on the 408 :)
Also people seem to figure a certain hp per cid say like 1.25 hp:cid is the same difficulty no matter displacement eg.. 273/340 hp vs 408/510 hp, obviously the head flow requirement between the two is vastly different.
