Was the image right side up before redoing the connector? That video harness itself, would not cause the image to flip. You have three choices:
-look to see if Galaga 88 has a dip switch that can flip the image.
-pull the monitor, and rotate it 180 degrees, problem solved.
-flip yoke wires: Caution!! If you don't know what you are doing with this, let someone more knowlegable do it for you. You can really screw up the monitor if you do it wrong.
Oh, and need to know what kind of monitor you're working with. Clear pics from the back of the machine, if you are not sure.