The LQ4 heads are 317 castings which flow almost identical to the 243’s that are on the LS6 motor (read: flow a ton better than LS1 heads). They have larger chambers which keeps the compression ratio down (good for this project obviously) and make great power. They share the same crank and all other parts, the block is iron instead of aluminum (~75lbs heavier) and the bore is larger. They generally make a little more HP/TQ than the LS1 with the mods being equal.