Welcome to the forum. You should have no problem towing with the 6 liter. What transmission are you going to use? Going after 450 will just add to the cost, but you can do a cam and spring swap. http://www.ls1truck.com/forums/front...in-budget.html
A friend has an LQ4 6.0/4L80E in a 94 Suburban and he tows regularly with no problem. The only thing he has on the engine are headers and a tune.