Hey Ratabase1,
I have a similar cocktail (Space Invaders) that I recently purchased. I'm in the process of altering it.
I already removed the left/right controller and I'm going to seal that hole w/bondo. I'm going to drill a new hole directly below for my replacement ball-top joystick, which will have the rotating 4/8 restrictor. I'd access the restrictor by cutting out the a hole in the wood below the cp--I'd make a thin cover for this opening.
I'm keeping the original button and adding one to the left. I'm going to use black pica control panel cover from Happ to finish it off.
I'm probably not going to use that black metal panel beneath the top one since it has metal I'd have to cut off (the part that held the original left/right control). So, to secure the top original metal cp, I'm going to place 3/4" wood strips on each side of the original control section that I'd screw the metal cp into...somewhat difficult to describe.
I think the most painful part will be drilling the holes into the metal, but I have done this before on my Dynamo cp. I wish I knew someone w/a hole punch, but I'll have to make due w/my drill and 1.125" metal hole cutter (purchased from Lowes).
On the same subject, I already installed my mobo, speakers, sub, power supply and coin door/cp lights to pc power supply. I am picking up the monitor and getting a new tempered glass top cut locally next week. I'm debating whether or not to installed new vinyl or venner for the exterior.
I'm curious what your plans are.
Good luck!