Cabin heat muffs are still used on general aviation aircraft. I have installed several.
I have also built a couple using aluminum.
It will have an intake air source and an outlet for heated air after it has passed through the muff. Then through a heat resistant scat tube to a flapper box on the firewall which lets the heat into the cabin or dumps it out into the engine compartment. It is activated with the usual push pull type control from the dash.
To have a look at one go to www.vansaircraft.com. Click on web store, then cabin heat muff, Part #Vent DL-05. The Heat Selector Bypass Box is Part # TG-10. Unfortunately these are designed for 1 3/4 inch exhausts and would have to be adapted. It is important to always have air going through the heat box to avoid damage to the exhaust pipe. Although these would not work without adapting because of the exhaust pipe size, it gives you an idea on how it would work.

Where Are You From? Kamloops B C

Do You own a car built by Durant? 1926 Star Depression Pickup

I have the sales brochure from Torrid Heat listing their heaters for Durants. I'm looking for a regular inside firewall mount Torrid Heater for my 28. Interesting concept.

Where Are You From? Oviedo, Florida

Do You own a car built by Durant? 1928 Durant Model 65