I see that everyone has neglected to mention the Stewart Warner Southwind gas heater.
"Heat in 90 seconds" was the company motto.
Don't have to wait for the engine to heat up.

The 781-B was the model for your truck.
Great Art Deco styling.

From $50 in need of work and missing parts to $250 completely restored and all the installation parts included.

Used Southwinds in everything from snow plow trucks to VW camper buses here in New England.