Welcome to the Stovebolt Stan!
You might want to post your question in the panels and burbs area. Someone there may know.
I saw a '41 at a car show a couple years ago, but I don't remember seeing any earlier.
I know a guy with a '39 GMC panel and another guy that has an early Suburban, I think its a '37, but don't recall exactly. Both of them hang out on the oldgmctrucks forum.
