I hadn't been keeping up with this thread, but I was going to say the r and g on the temp switch sounded like it was for a car with lights. R goes to red hot light, g goes to green cold light on lots of 60s cars that didn't have temp gauges. My 67 Ford Fairlane is like that. Cold light is on below 100 ish degrees, hot light comes on like you'd expect.
Lots of gm temp switches are set to 260 to 275 because they screw into the head usually and coolant temp is actually warmer there near the exhaust ports. 275 in the head is about 245 to 250 at the thermostat, because it's still mixing with "cooler" water that isn't near the ports. And at 13 to 15 psi with proper antifreeze mix water won't boil til 275 or higher. An engine isn't technically overheated until the coolant is boiling, as long as it's still a liquid 275 coolant is cooling the much hotter metal, which around an exhaust ports can be way hotter. I understand the wanting the hot light to come on sooner, it does give a safety buffer, but that is GM's reasoning.
That makes sense...didn't even think about the old 'cold' lights! I still haven't found a spot for the temp switch yet, but I haven't messed with the heater core/defrost yet either so those will probably happen at the same time.