Toddle, I found this info in my basement today, it explains the manifold heat on your '38 McCulloch supercharger. It's not an original, it was reprinted in "Ford Life " magazine back in the '70's.
Well I've tried to include scans but can't, I keep getting a prompt about a "missing security token" whatever that is. It seems to complete the uploads but then the error shows.
Here's a synopsis- the exhaust manifold heat passages are included in the McCulloch manifold to provide automatic heat control. The new 1938 design is the first in America to control the temperature of the incoming mixture automatically. A thermostatic element is placed directly in the intake passageway and operates a butterfly shut off valve to limit the flow of exhaust gasses through the jacketed rotor housing. The result is amazingly rapid warm up, smooth acceleration, and maximum top speed performance.
Their claim was 124HP on a stock '38 flathead when installed with the dual exhaust system furnished at no extra cost.