That will not be a factory built 4x4 truck chassis. It was sent to some 4x4 specialty shop for the 4x4 conversion. There were several companies back in those days that did 4x4 conversions on various van chassis. The two most common conversions are on Dodge and Chevy van chassis. It is very rare to find a Ford converted like this.
Dodge did build a factory 4x4 W300, one ton truck back then. However, those have a completely different chassis/frame under them.
That is one neat RV. I would love to have one and you are very lucky to have latched onto it. Congratulations on a great find.