The neck carving on my D80-12 is different than those on the JF100, JF100-12 and D100. The D100 also seems to be more lightly built than the D80 and D80-12.
Seems to be one more corroboration of the many observations about Guild having gone toward the "built like a tank" style from the mid-late '70's until the mid '80's and that when Gruhn "came on board" (early '84) with revamped dreadnoughts and the F44/F46 he instigated a mover back towards lighter builds, and then he himself became an owner for a short period (late '86-'88), and instigated the "notorious"model number changes like the JF65/55 to replace they F50/F50R as well.
Cosmetically they look very similar, but I am sure a deep dive will reveal some other differences, especially since there was not only a few years that separated the production dates, but also ownership changes in the company.
And there are very subtle differences between the JF's and their predecessors, much like we see here between this D80 and the D100's. Wouldn't surprise me at all to see a bracing difference, and that's pretty darn deep and "invisible" on the surface.
It'd be very interesting to see what internal pics of the bodies revealed.
I wonder if the soundhole reinforcements, are different too, as described here by member Dapmdave chronicling known bracing changes on dreads from the '70's-'80s:
http://www.letstalkguild.com/ltg/entry.php?14-Guild-dreadnaught-bracing-patterns-1971-1995
And then there's that bridge (possibly another Gruhn idea like the snakehead headstock?), and the frets
do look noticeably "fatter" than the D100's on pg. 7 in the '96 catalog.