This is the layout I'm thinking of using:

The top layer, in order, is plyr 1 start, plyr 1 coin, spinner ........... pause, plyr 2 start, plyr 2 coin, exit
Things look off for some reason in the spacing for the joys/buttons/trackball.  I can't figure out why.  I've gone over the math several times.  Maybe it's just an optical illusion or something.  Here's what I did:
The panel is 38.5"w x 15"h.  The bottom of the trackball and the bottom of the lowest button for each player is exactly 6 inches from the bottom of the panel edge (for hand/arm support, as well as allowing steering wheel clamp on).  The center of the player 1 joy is 4.5" from left edge.  The last player 2 button is 4.5" from right edge.  From joy to button on both players equals 6.75".  So, from edge to last plyr 1 button is 11.25.  And from edge to player 2 joy is 11.25.  That means it's 8 inches from the middle of last plyr 1 button to center of trackball and 8 inches from middle of plyr 2 joy to center of trackball.
Everything should be perfectly aligned and centered.  But it looks off, doesn't it?  I think it's just because the joystick throws it off.
Thoughts?