Jim, ultimately it doesn't matter which way the coolant flows in the heater, the core isn't "directional", just need both hoses hooked up, and heaters were an option that weren't included in the "standard" models or the shop manual, the instructions for those are in the accessory booklets ... and of course we know that GM didn't find it necessary to 'hold the mechanics hand' like Ford did, they trusted their wrenches knew which way the pump pumps
Bill
