Dean - that link I sent you has several ways to hook up a "LS" cooling system. I don't have a SL-coupe here (yet) to see the logistics, but the radiator being so far away from the engine presents it's own unique circumstances. I have a LS-6 in my stalker and I am using a pressured/sealed configuration (no heat or a/c) with my steam vent coming off the engine and plumbed back into the upper radiator hose. It's not the proper or best way for hook-up, but at least it's moving any steam/pockets of air from the heads. The pressurized system expels air after several heat/cool cycles and one must re-fill and keep an eye on the coolant recir. tank and fill as air is expunged and coolant drawn back into the system. I am really space limited or else I would have done a more proper routing. Hopefully someone here with a coupe and more knowledge of the LS will jump in.
Regards, Sharkey