That heater depicted in a previous post is a Ford (OEM) heater.
The truck heater appeared very similar to the car heater. However, they mounted differently, and the inlet / outlet nipples were in different places than the car version. The truck version had a small drain plug at the bottom, the car version did not.
Also, '39 heaters had squared of knobs vs. the rounded version in '40.
The '39 heater body was a brown color vs. gray in '40. The toe guard in '39 was solid, in '40 it was vented.
Noi stripes on a '39 heater, the '40 heater had three red horizontal stripes on its two sides. These stripes were approximately 1/8” wide and spaced approximately 5/16” apart.