Doug, you work yours just like I do. I'm thankful for the heat this time of year. In my 79 I just leave the adjustment at full on, and like you say, the fresh air intake does the circulation fine once warmed up inside. If I notice it getting stuffy I just hit the recirc button and the flow stops. By the way, the 79 has that same cold air vent on both sides, not that I ever reach over and fool with the one where I guess your lambda 'computer' resides.

When I changed the valve, (an 84) I brought a cake pan and some old towels. I let the block drain first and just held the hoses high while I worked them loose from the old valve. Only got an ounce or two in the pan, and a few drops on the towels. The cake pan might have held all the coolant in the core, but it would have been close. The 20 year old hoses inside the car looked like new outside and as far inside as I could see. I don't own any hose squashers, but I admit to using a vise-grip plier on the transfer pump output fuel line once.
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Art Benstein near Baltimore