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Welcome Jim
Sorry I can't help you with your pre-heater but I am sure one of our members can. I have a 1967 337B normal asp. and I live in Oklahoma and if it is to cold I don't get the plane out of the hanger !!!!!!
You might give us some more information about yourself and your airplane ie, where do you live (you can put that in your profile) and why you purchased a skymaster, etc.
Again welcome
Fred N358

PS you could attach a picture of your aircraft.