Echelon said: what kind of special neck did he want?
i always thought the jag-stang neck was always based around the "baseball bat" style neck on one of Kurt's vintage mustangs (he chose the one he found most comfortable).
Fender then took his guitar away, and exactly replicated the neck..i.e. the one on the jag-stang is EXACTLY want Kurt wanted.
Yeah, that's what he ended up with, but his sketches show a few various different configurations. Most of them feature Tune-O-Matics, some have hotrails between the two pickups, some have different headstocks altogether, some have Strat style jack sockets.
Let me take a picture from Journals of the headstock I liked best...
Big images: http://img179.imageshack.us/img179/9989 ... ch1mv5.jpg
http://img158.imageshack.us/img158/9926 ... ch2so7.jpg
Cropped:

The first of the big images is the one that resembles the Jag-Stang as we know it most closely. It's interesting to note how he anotates "preferrably jaguar tailpiece and tune o matic bridge
or whatever is simplest". Clearly Fender took him up on the "whatever is simplest" offer and whacked a Mustang tailpiece in. He also asked for the convex curve on the back for playing sitting down, again, Fender didn't put this in. The humbucker he wanted was an SG Les Paul one. He wanted a Jaguar single coil in the neck. He said "If this Headstock isn't possible, then the old Fender headstock will be fine". I definitely prefer his version.
It seems ultimately Fender chose to cut some corners and go with his cut and paste photo version. It's a shame really. I'd really love to bring one of the REAL Jag-Stangs to life at some point, especially with that awesome headstock.