The GB75 neck measurements are as follows:
Width at nut: 1 3/4"
Width at 22nd fret: 3"
Back of neck to top of fretboard (as best as I can measure): 3/4"
The neck of the GB75 is what I consider a flattened "C" shape. In the neck profile image below (although really for gui***) it appears most like the "D" shape, only thinner back-to-front. A comfortable neck to play on, just a bit wider (side-to-side) feeling than a lot of uber-skinny necks that I've played before. But then, I find more space is better for slap technique for sure.
FWIW, my A5 has the same 1 3/4" nut measurement, but only widens out to 2 5/8th" at the 24th fret. So, both necks start the same width at the nut, but the GB75's neck spreads out roughly 1/4" more by the time it reaches the 22nd fret.