Some old cars did use the running boards as the antenna, I can't remember which ones, but I do remember looking at one set up like that.
Also remember seeing an old ford, 30's with the fiber top. The top has a mesh of chicken wire in it that not only provides strength for the cloth part, but also acts as the radio antenna.

I have never seen one used, but I will look into one of the hidden antennas for my project. I think it can be mounted above the headliner?

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-