Sorry if I missed a joke somewhere, but the Space invaders cab seems like a bad cab attach to a 4-player CP
If you are not going to tear out the monitor, mirror, bezel, etc., then the display seems like it would not be great for 4-players to crowd around.
If you are going to tear out its guts you may have to build so much into it that it may be better for you to start from scratch, or start with a 4-player cabinet. Also, it in the picture, it looks as though it isn't so far from restoration, so you-know-who might kill a kitten.