Well, I have traced the body of my RG7, which is more or less the same as the JEM.
The dimensions of the handle, the lions claw and the jack placement you could take from the tutorial section on the main site.
There´s a very detailed blueprint of the JEM body (old style neck joint) somewhere over at Jemsite.
I just have a (pretty accurate) drawing of the 7 string headstock
Placement of the pickups, trem, controls and the neck should be determined depending on the scale and the situation of your build.
If you are interested in the drawing of the body and the headstock you can PM me.