Greetings OnWheels! Welcome to the Forums and the world of Vintage Airstreams.
Your trailer certainly raises many questions in its model identification. It is not an entirely unfamiliar circumstance within the Vintage Airstream community as the 1950s and 1960s were a time when Airstream seemed to nearly encourage customers to special order trailers to meet their desires so it is not uncommon to find unusual features not mentioned in literature of found on other similar models. The original owners of my 1964
Overlander Land Yach International ordered it with hydraulic drum brakes because they already had their 1957
Mercury outfitted to tow a trailer with hydraulic brakes. They later converted the trailer to electric drum brakes when they purchased a new 1967
Mercury, but some of the hydraulic components were still on the trailer when I purchased it in 1995.
The size certainly says Overlander, and the single axle does not necessarily preclude that. I have friends who have a 1960 Overlander that was purchased new by his grandparents and it is a single axle. I do not know whether there was any difference in the serial number because it was a single axle.
The one unusual feature that I noted in your phots is the placement of the porch light fixture base. It is located above the jalousie window while the more typical location is near the bedroom window. I am attaching a photo of the porch fixture attached to the side of my 1964
Overlander Land Yacht International.
Good luck with your investigation!