I bought a couple of 2 wheel trailers, The red Ford one should be a late '30s maybe even a '40 Ford what is the gray box?
The gray box has a T front axle under it (2 wheel trailer) could the box also be a T?? maybe a TT? Just thinking someone built the trailer out of common parts. The T hubs were drilled to take steel wheels, pulls nice!
Based on my own experience from ordering the wrong thing, on the 48-mid fifty F-1, the chain locking tab is located in the tailgate "curl" at top. The later (mid-fifty to 52) is riveted just below the "curl". Based on that I'd say the red one is 48 through mid fifty.