I got the galaga cabinet when it came back on sale in September. When it eventually arrived and assembled it, I played it for 5 minutes until it broke. The plastic joystick and buttons was a joke.
So I had some hole saws but could not anchor it to center the drill bit so I added some bondo to the slot and let it dry for 2 days. Then I made a 1 inch hole with the saw and added another button to the side of button A.
In order to keep the CP artwork from getting scratched up I used blue painter's tape and covered the CP before drilling and I drilled from the reverse side very slowly. Go on the 1up website and order a free protective film. Don't use it. Use it for a template and make yourself a better control panel later on. You will be surprised how many vertical games there are on mame, but more buttons means more games. You might want to add a spinner or trackball. Why not? There is plenty of room.
Where the switches are above, I replaced them with buttons (same process) for two player Select. Replaced the joystick with a Happ Super Batt and buttons from a previous project.
Then I added Retropie after modding the cabinet courtesy of ETA Prime:
I went with the LCD mod, but on hindsight would have saved a few bucks by de-casing a dell 17 inch monitor. Doesn't really matter as you can get decent sound from the LCD board and USB speakers.
I got the joys and buttons
pretty cheaply and they are really good lit up. The encoder is fast.
Keep all the old parts and CP incase you want to sell it later on. Keep the box it came in too. Prices for these cabs are on the decline, so you might want to buy a street fighter or Asteroids for the horizontal games. If you got the riser, you need to get better supports as the ones it came with are uneven. Nothing worse than a rocking cabinet.
BYOAC the ---steaming pile of meadow muffin--- out of it and post your project when completed. Have fun.