Sounds to me like you are over complicating things. Do you have the maifold warmer hooked up to the radiator hoses? The manifold has a port in it with pipe fittings that route warm water from the engine to the radiator. This warms the carb and whatever else. Moreover, it sounds like it is a simple choke adjustment. The choke is staying closed longer than it should. The auto choke has a spring inside that is heated by a power source from the key. As it heats, it allows the choke to come open. If it isn't getting warm enough, it holds the choke shut. By loosening the screws that hold the plastic cover, you can rotate the housing, changing the tension on the spring. When the enging is cold, the tension on the choke should make it just close, and no more. This will trip the fast idle cam and it should purr right along.

Leonard

57 444 b20/m41 (with 32/36)