Sounds like you have a grip on the geometry, that was my concern. Back to the splines, the HD black Hitec servo wheel may work for what you have in mind. The way I would do it is with some .062 aluminum or CF but do a double arm having one on the bottom of the wheel and one above and put a ball link between the two. This would load the servo output shaft more evenly so that the load is not concentrated on the upper half of the splines.