This may be trickier than you think. I sort-of "collect" interesting shapes. as do some other people here, and one of the consequences of that is I have developed an extremely healthy respect for just how eye-appealing the original Fender Strat, Tele, P-Bass, Jaguar/Jazzmaster, and Jazz bass shapes are. There have been a number of people over the years who have tried to put their own little mark on the jazz bass shape - Wahl is one of them, Sadowsky another, and man, you change one little bit of it a few millimeters this way or that and it can get ugly kind of fast. Mostly, the upper bouts get too fat. To make a guitar, the first biggest difference is how far you want the bridge from the neck pocket; then all your other changes move from there. You could try printing a few schematics from one of these guys:
http://shortscale.org/forum/viewtopic.php?t=38813
http://www.gitarrebassbau.de/viewtopic.php?f=10&t=6&start=0
and break out the pencils & french curves and see where you get. If I were to try it, I think I'd approach it more from the point of a Jazzmaster shape with hornier horns, because changing the scale length from a jazz bass 34" to a guitar 25.5" by moving the bridge 8.5" is going to leave you with a huge ass and all the stuff clustered right up toward the top.