The reason to use a big block for towing is cooling, not raw torque. A small block pushed as hard as the LS1 has difficulty getting all the heat out of it. Sure, it will pull hard full throttle in a drag race, but it takes a big block to be able to pull full throttle for more than a minute or two without overheating.
There's a reason big blocks are used for things like swamp fan boat motors- they still run cool when pushed hard.
