Re: Peter Green Mod only using wiring
The Fender that "always" had series pickups that could be run out of phase was the Duo-Sonic II. This is not the first version of the Duo-Sonic, which pre-dated the Mustang, having come out in 1956 (of which the Musicmaster was the single pickup budget version). This is the second version, which was re-oriented in the product lineup to be a budget Mustang, when the Mustang came out.
The Tele wiring that we call "vintage" (although it was NOT the "original" Tele wiring) had the following switching options: 1) bridge pickup without tone control, 2) neck pickup with tone control, 3) neck pickup with treble removed. The Esquire had: 1) bridge pickup without tone control, 2) bridge pickup with tone control, 3) bridge pickup with treble removed.
The Tele wiring that we consider normal today was a 1967 introduction (though people had been doing similar mods themselves for years in order to get both pickups together in parallel, and/or a tone control on the bridge pickup – e.g. Steve Cropper).
The 4-way switch is a relatively recent introduction. I didn't hear of one until about 10 years ago, though they were probably around before I heard of them. It's usually wired so that the extra spot gives you both pickups in series, in phase. The Baja has a 4-way, and a switch that puts one pickup out of phase, which can be used with the pickups in series or in parallel. In other words, the Baja gives you all the typical Tele options, plus the Mustang and Duo-Sonic II options (parallel in or out of phase, or series in or out of phase, respectively).