Adorshki,
Thanks for your info!
If I read you right, you're saying the JF-65 is basically the same as the F-50?
They just changed the model designation to signify George Gruhn's involvement at Guild?
As I understand it Gruhn was responsible for the revamp of the model number system, it was intended to bring consistency to the system but seemed to cause some confusion instead.
He also brought in master luthier Kim Walker and introduced some new models.
"basically" the same is the important qualifier there.
Like Neal said, it wouldn't surprise me if bracing was slightly changed under Gruhn/Walker, it was part of their self-defined mission to improve the line, but I can't remember specific references about F50s/JF65 bracing, although for sure we know it changed on models like D55's, and not just under their stewardship either.
Later versions of JF55/65 got abalone rosettes for example.
Some versions of F50 had ebony fretboard and rosewood bridge, but
http://westerlyguildguitars.com/guitars/f50.html shows JF65 with ebony bridge.
Also I think at least some versions of JF65 got 3-piece laminated necks (resists twisting), but I don't know if that was true of all F50's, I seem to recall some of 'em had one-piece necks.
So the basic formula of size and arched maple back/sides remained constant although little details could change.