Despite the second trip back to Joe, the stock came back just the way I wanted. The wedge fit solid in the dovetail and the ball detent snapped positive in the both cutouts to lock it in an extended position.
Per my request, Joe also replaced the roll pin that attached the swivel plate to the main tube. While the substitution undoubtedly improved the overall esthetics of the stock (not to mention staying true to the original design,) it somehow lessened the tension required to lock the buttplate in the downward position. As a quick fix, rather than shim the spring, I decided to replace it with a trimmed mainspring from a 1911. Doing so solved the problem.
Then, I noticed something else when I attached the stock and shouldered the pistol. The action caused rearward pressure that pivoted the grip slightly forward. To make matters worse, the movement was just enough to bind the trigger bar's movement and hinder sear reset once the trigger was pulled.
With only a single screw holding the grip in place, the discovery really wasn't too surprising. While it offers tremendous credibility to my buddy John's suggestion for a frame-mounted dovetail—no John, I still haven't ruled it out—fellow U.N.C.L.E. Special builders Paul and Eric recently approached me with a possible solution to stop the grip from pivoting. They ran two small pan-head set screws from inside the mag well into the grip thereby pinning it to the frame.
Right now, the notion of this quick fix is much more appealing. However, to play it safe, I plan on compiling some dimensions in relation to John's idea, should it become necessary down the road.