Yes, Galaga and Ms Pac cocktail are the same. Yes its possible to
convert the galaxian, but its a little bit of a pain. You will have to
do some woodwork to accommodate the Pac panels.
I was just at the arcadeshop website, and saw that they sell a metal
control panel that will allow you to convert a Galaxian to a Galgaga
or Pac Man. They have a picture of the bare metal panels, but not a
picture of what it looks like on a machine.
Mspacman,Galaga,Super Pacman ,Fire Fox and a lot other Midway game,use
the same cabinet,same size 9" control panel .
Galaxian and Pacman use same cabinet,same 11" steel panel but the wood
panel part are different,Pacman is deeper,you can make it works but it
will not fit in a standard joystick ,Midway or Wico joystick unless
you cut a hole in the lower part of panel,some small imported joystick
may fit.