I took some pics of the Gamecab yoke, hope these are useful.
Pic 1: The design is somewhat similar to the older DIY yoke, but is built with sturdier parts and includes stops to limit rotation. As you can see, the hub of the yoke has a long horizontal shaft running clear through it, with two shaft collars screwed on just inside a metal enclosure. These stop the shaft from moving laterally. Two thumb screws threaded into tapped holes in the collars limit rotation in either direction to a total of about 50-60 degrees (haven't measured.) A third thumb screw is threaded directly into the back side of the shaft, and is drilled to allow two springs to be hooked on and center the shaft rotation. A set of gears link the shaft to a 500k potentiometer. It appears to be a 2:1 gear ratio.
Pic 2: The shaft exits the enclosure thru 2 bronze bearing sleeves that allow it to turn smoothly without any play. The enclosure is 4.75" wide. 2 short pieces metal tube are attached to the shaft onto which the Happ grips are assembled, one tube is welded, the other (pictured) is merely press-fit onto the shaft and secured with a machine screw. This seems to be just as solid as the welded end and is how I intend to reattach the handles when I make my mods, but the hole I drill for the shaft will be at an angle, so that the handles will be in a more ergonomic position. This will definitely involve a drill press and a clamp.