I agree, it is a 55'-57' Overlander/ Crusier or Custom which are all considered 26' footers measured bumper to tongue.
In the mid-late 50's which this trailer definitely is based on the number of panels at the end cap, Airstream didn't offer a 24'. The bumper & tongue add 2-˝ to 3' to the body though which is where length confusion comes from.
In '58, the end panels were reduced from 13 to 7 - so it has to be earlier than that. In '54 the rear tail lights were square. If you post the VIN number, you can be more certain.
1955
Ohio built:
O- 4183 to ~O- 4219 (Cruiser)
O- 7000 to O- 7144 (Cruiser “Overlander”)
O- 4600 to O -4609 (Cruiser “Romany”)
California built: ~6500 to ~6600
1956
Ohio built:
O-7145 to O-7358 (Overlander)
O-4219 to O-4233 (Cruiser)
California built: 6NNN
1957
Ohio built: O-7359 to O-7593
California built: 6NNN
(~6700 to ~6900)
Shari