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My '52's OEM switch has ACC position. Can you post a pic of the front of your switch? I may have one. (48050's are different than 51-52 at the opening in the dash)
Here's a few more pictures of the switch. As I mentioned earlier, there are three positions although there are no markings to indicate what they are and the key can only be removed in the center position. Not sure if it makes a difference but the truck is a late '50 with the '51-52 bed.
Ok, that looks like an early Cole-Hersee aftermarket ignition switch. They were a universal switch with a threaded bezel. They are still made, and now available with a start function and several other features as well.