I don't disagree that double shear mounting is a better arrangement, but how much is the cast iron housing and hardened steel shaft of a steering box flexing compared to the thin stamped steel and spot welded structure of the F frame and box mount? Have you watched a steering box moving around while being cycled through the steering range? The flex of the box within the mounting system of the k frame is a much greater detriment to steering response than deflection of the steering box and pitman arm. You can reduce that flex via a double shear mounting on two planes by supporting the lower end of the box, or by reducing the flex inherent with the mount. Either way are very effective at improving steering response. One requires an afternoon of effort with a plasma cutter, grinder, and a welder, one requires an hour with a drill. Both achieve the same result.