The highest output 6.0L motor will just match the HP of an LS1. You get more displacement but with the cost of 65-75 more lbs of weight to have to lug around. The 6.0L can be bored over a little bit but the cost of good machine work is about the same price as buying a new LS1 bare block when needed. 400 hp is simple to get from a LS1 with bolt-ons. Can you tell I am a little biased?