That's the size our 59 would have used also. Somewhere along the way a new battery box was fabricated to fit a more conventional/current sized battery. I had at one point throught the narrow box was for a pair of 6v batteries that would have still been very common durring the time.
Since our original box is missing and the current box interferes with how large of propane tanks I can run as well as being in bad shape, I'll be relocating the battery. My plan is to make a tray between the frame rails like current A/S models are running I may atempt to fabricate a aluminum cover.
I intend to take photos but that modification is a ways off at this point. I'll post up when it's done.
1959 22' Caravanner
1988 R20 454 Suburban.