New guy here "66 4x4 sort of

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Hey guys, new to the forum but not forums. I just purchased a 1966 4X4 C10.
Yes I know. The first letter of my serial number is C not K. Thats ok the build appears to be done well. It is a 292 4 speed. This is a very solid truck. Cab, bed, frame, and driveline in very nice condition. My question for youall is about the transfer case. It only has hi (all the way up) and low (all the way back). Any idea what unit this is? Part or model numbers? Years in production?
any and all useful information is greatly appreciated.