I wanted to build a jazzmaster at first. But I have a soft spot for the mustang, so I initally wanted to combine the two. Instead of Jazz pickups, I went for p90s (tonerider vintage). These pickups and the Thurston Moore signature Jazzmaster inspired me.
The body is thicker than a mustang body, it is the same as a jazz/jag because I decided on adding body contours.
It took me a while to decide whether to have angled pickups, like a mustang. The mock ups I made looked better like this, and I'm not convinced it effects the sound too much...so I went with it.
Bigger p90s were a bit cramped, plus the availabilty of short scale necks, lead me to design a full-scale guitar (same as Jazzmaster).
I designed a jazz style pickguard, but the mustang guard meant easier construction (although had to extend it to fit the scale). Switching was always going to be simple 3 way toggle...eventually on the lower horn...although I considered upper horn and in the jack socket hole/chrome plate and having the jack underneath the body.