I have an old Galaxian cab I'm converting to a 48-in-1 (don't worry, it was empty and converted like six times before I got to it). As you can imagine the control panel is completely swiss-cheesed.
I envision the joystick in the center, with three buttons on each side of the joystick in a triangle pattern. That way it's good for both lefties and righties. P1 and P2 start would be in the same place. And of course the holes for the wooden underside would be where they're supposed to be.
The more I get made, the cheaper the per-unit price would be. Likely around $50 per.