pierce-
I've got a fairly stock 1937 Chevy 1/2 ton pickup and I have never found the correct piece for that spot. I have been told it is a piece of windlace type material covered in a vinyl or leather of a color that would go with your truck, probably black. I had my upholstery guy make two for me. Basically they look like large pieces of fender welt. They do work good and look good, but I'm not sure if they are correct. I think the 38 truck has the same situation.
I'd like to know if you come up with some more solid information on this question.
Thanks,
Joe