I've got 5 gallons of Quinsyn Plus compressor lubricant/coolant, from what I can find on it, it's a 30wt non detergent synthetic lubricant. Would be willing to part with it for a reasonable price being as I have no use for it. I know it's designed for twin screw compressors so it might not be...
I know on quite a few GM pickups they have don't have petcocks on the radiator, just have to pull a hose and let it drain. The transmission spec you found is probably just a drain and refill.