Here's a potential oddity for your consideration.
The pictured tunnel is molded papier-mache, is 15" long, is not labeled on the inside, and has no decorative buildings or roads, etc. on its sides. It features a relatively simple two bump design scheme a la Gilbert. Another knowledgeable Flyer collector friend and I believe this to be a No. 248 from the circa 1938 Gilbert period fabricated like an AFMCo. tunnel. There were numerous manufacturing techniques carried over from Chicago to New Haven during the transition. The coloration is consistent with AF for this period, but the rectangular openings do not fit the theory. It is not Marx, Lionel, or Jefferson, so by the process of elimination we are back to considering prewar Flyer. Another possibility is this is a separate sale piece by a subcontractor for American Flyer. "Side 1" and "Side 2" are shown below. Suggestions and comments are welcome.
Have fun!
Bob
