Cross, you're right. There is a difference.
This picture doesn't show it very well but on the bass, where the neck bolts on the body, the lower horn starts its curve a little sooner than on git-tar. The inside upper horn on the bass also curves in a little sharper than the guitar.
I wonder if this was done on purpose? When you look at them side-by side the lower horn on the bass looks a little clunky, IMO.
The guitar is for sure a Dec '65, I took it apart once. According to the Fender Bass book, the bass is somewhere between Jan. And September '66. I've never taken it apart and won't if I don't have to, I'm too chicken ####.
Here's what I used to trace them. A graphite stick filed razor-sharp on one side. 
The flat part of the graphite stick presses nicely against the guitar body. Precision! I should have been an engineer. I slide a piece of post-it-note around the stick so the tracing is actually .0001" thicker, but I'm sure you can make that up when you're cutting out the template with the band saw.
Sorry for the late reply. I should have said from the get-go it'd take me so long to reply you could time me with a calendar. What's that John Lennon quote about life is what happens when you're busy doing something else? I thought about scanning in the bodies and posting them to show the difference, but that would take another week or three to get around to it.
Anyway, you can pm me your address and I can send you the tracing.
Should the be moved to the Mustang page?
