After just now downloading the OpenSCAD file, I noticed a visible difference between the STL model and output generated from OpenSCAD. I can only assume the MCAD/involute_gears.scad library has been modified since this thing was first published.
In the source file: "Gregs_Accessible_Wade_Herringbone_Gears.scad", lines 89 and 90 read:
g1twist = 360 teethtwist / t1 / 2;
g2twist = 360 teethtwist / t2 / 2;
By removing the divide by 2 factor, the OpenSCAD output now appears to exactly match the physical gears on my current machine:
g1twist = 360 teethtwist / t1;
g2twist = 360 teethtwist / t2;
Long term feedback: After a few years faultless service of a set of these (11:45 ratio in PLA) on my Prusa Mendel, I'm just about to integrate these gears into a derivative of the seminal Mendel90 by Nophead.
Thanks again for the great design triffid_hunter! :)