Sorry for the late reply, guys.

One thing though ... I reckon you should ditch that flimsy piece of tin, and go for an industrial strength MDF wood control panel.
Well, the Sigmas are about the sturdiest super guns on the market, so a flimsy piece of tin, it is not. And, I hate wood, so that idea is out.
I see you got the top off of your stick so you could access the screw that holds the shaft together.
I used a 9cm wrench. Nothing fancy (at all). It's the kind of stick where you can reach the nut from the top. The sticks in an original control panel (at least one I've seen) are covered on top, and require a small screw driver to open up from the looks of it. Although I've not tried.
Now I need to find a spinner to play some Forgotten Worlds!