Just say no to the 6.0 iron block. An iron LS series (LQ-4 and LQ9) are heavier than a SBC. They make great power and are very strong but the weight kills most of the LS's advantage.
The LS2 is the aluminum version of the 6.0 and is the hot ticket. But if you have a small bore (3.898) LS1 it will perform better on an airboat than the iron 4" bore. Both great engines, just one's a hands-down winner on an airboat.
Felber