I wouldn't mind seeing how you made that center stick mount.
well I'm very unskilled when it comes to this stuff so it was a discover as you go process...here's what I did:
measured the distance between the legs of my chair and made that the diameter of my joystick mount base
measured the distance from the ground to the base of the actual joystick for height and then subtracted the width of the plyboard used for the base and the round joystick pieces.
used two 2x4's and set them in a "t" configuration and nailed them together after I cut the proper lengths.
found the center of the plyboard base and nailed the "t" configuration 2x4's to it.
the round joystick bases gave me the most trouble as I had to keep the screw holes aligned properly while I nailed them to the 2x4 vertical part.
Hope that helps in some way.