The Fender Duo-Sonic was launched in 1956 as a dual pickup student model with a 22 1/2" scale neck as standard. The guitar was significantly redesigned in 1964 as the Duo-Sonic II, gaining a new body style, totally new hardware (largely in line with the Fender Mustang), and a 24" scale neck. The original three quarter size neck was still optionally available.
The service sheets reproduced below refer exclusively to the post '64 Duo-Sonic II. It was produced as a single folded sheet, with five pages of content. All parts are listed as well as a simplified circuit schematic and part assembly blueprint. All in all a very useful reference item, for anybody attempting to identify and replace a missing or damaged component on their guitar. Compare also, with the simple part list issued in 1969 here.
This sheet also details the factory string set for this guitar. The set suggested is .012 - .052. Remember this is a student guitar! Few young guitarists would get very far on such thick strings today. The suggestion for the 3/4 size version was the same strings, but cut to length.