This is now my oldest 35mm camera:
This started out as a Leica model I - the first commercial 35mm camera, made in 1929. Probably in 1932 it was returned to the Leitz factory and upgraded to the new model II, by removing the fixed-mount 50mm Elmar and adding the L39 threaded mounting flange, modifying the lens to a threaded mount body, removing the original viewfinder, accessory shoe, etc. - and installing the new combined Rangefinder / Viewfinder unit with linkage to the lens to make it the "automatic focus" Leica. It was called that because you turned the lens focusing until the rangefinder showed a single image, and the lens was then "automatically" in focus. (Previously you had to measure the distance with a separate rangefinder accessory, then transfer that distance to the lens.)
Leitz used to offer conversion of older models to the latest up until body changes for the IIIc model made that impossible. The model III, with added slow speeds to one second came out in 1933, so if this were converted after that it would likely have been made into a III. Many model I (also called model A) were converted for more convenient use. By now they would be worth much more if they had never been converted.
I didn't have either a model I or model II in my collection, so I got both in one with this one!