The intake manifold is your biggest issue. Between 40 and 60 is about the worst temp range to adjust a carbed motor. its too cold without a choke, and its too warm for the choke to stay on long enough to get past the lean stumble. Opening up the exhaust crossover in the intake would probably solve most of your problem.

Short of changing the intake, or setting up the choke more rich, the only other option is to introduce warmer air into the intake.
A few ways to do that, off the top of my head:
1, If you running an open air filter, get one that is closed for your winter driving. Restricting the amount of cold air available to the carb will help your lean condition.
2 Pull warm air off the exhaust and run it through the thermostat controlled snorkel on the closed air filter housing, if you have a dual snorkel housing, one heated snorkel should be enough to do the job. This will require a vacuum source for the thermostatic air door to open and close, and a tube attached to the header/exhaust manifold duct-ed to the snorkel.
3, If your running a heater core with functioning heat, you can pull a heater hose close to the carb to warm up the carb.
4, Another thought is that maybe you can run a copper tube filled with engine coolant between the bottom of the intake and the valley pan to warm up the intake. This could be controlled to shut off once the engine reaches operating temp.

#1 & #2 are better options. Gene