Just another dumb idea besides getting a 92C thermostat. Rip out the engine cooling fan and install an electric fan. Not only will that allow the engine to get up to heat faster, it will add about 5 more bhp :) Who needs a cooling fan when it is -20F outside? And when you are driving down the road, there should be enough air flowing through the radiator to keep things cool without a fan running.
Your 164 really doesn't "need" AC, especially at altitude and with the floor vents open. If you already haven't, remove the compressor to get rid of about 20lbs of dead weight.
I agree with the trash in front of the heater core, it is amazing how much gets accumulated when there is no air filter. This is true of all cars, but the dumb design by Volvo makes getting to it almost impossible.

Have fun and keep it simple,

Klaus
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The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)