I know that the science is not always easy to follow so here is another way to look at this.
GM and later GEP continuously worked on this rear engine overheating issue over the life of the 6.2 and 6.5 engines. First they changed the crossover design, then they added a dual thermostat housing, then a higher flow pump, in HMMWVs they went to a geared fan, then when all else failed to solve the issue they did one of the worst admissions of failure in recent memory. They oversized the bores of just cylinders #7&8 so that when they overheated they would not score the cylinder walls, break rings and seize up the engine! If you don't believe the science, believe the trail of evidence!
Later, GM in the development of the LS engines knew that they needed precise balance of the cylinder to cylinder temps so they could run lean enough to meet the stricter emissions laws and not cause detonation. They were able to get away with rear engine over temps in earlier gas engines by simply running richer but with added emissions standards could no longer do this. GM came up with what they call the Steam Vent. The Steam Vent is a coolant pipe which draws coolant from the back of the block and reintroduces it at the front to create better flow to the back of the block/heads. This is the same as we are doing with our kits.