I had RAM - K's for over 40 years. I found that an one inch freeze plug fit perfectly in the heat tubes that run from the exhaust manifokds to the plenums under the carbs. I blocked both ends off of the 4 pipes and drilled a 1/4 inch center hole in both ends that controlled (restricted) the amount of heat that went to the plenums. This was to prevent the full blast of heat to burn through. We all drive our cars in mostly warm weather so you don;t need a full blast of heat.
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300K,ly
Don Cole