Does it have the high idle solenoid on it, I had a 78 GMC Diablo (Still an A/G body) for a very long time and most of the time when I worked on any G body the thermostatic choke was out of adjustment and most were missing the high idle solenoid. I know everyone calls them Quadrabog or Quadrajunk, but if you understand them they are really good carbs. That said I never had to deal with the extreme cold you guys do, most of our winter consists of mid 40* temps, with the occasional slightly below freezing days. I switched over to a Manual choke Carter/Weber/Edelbrock Carb and never used the choke, I would just start it up and hold it at about 1K for a few minutes until it held when I let off the gas.
There is a setting on the side of the carb for adjusting the choke. Iirc there is a middle setting and hash marks for richer or leaner and a heated tube that passes into the manifold with a couple tubes that enter the front and rear of the carb. See if everything is there still. You can add a relay to turn on the solenoid to hold it at a high idle when you start the car. It's the same solenoid that is used when the AC is turned on.
Jeff
