The difference is:
1) A Galaga harness has two less pins placed in the molex connector as there is no up and down.
2) A Bosconian has two fire buttons (both do the same thing) so the harness wires go to two fire buttons.
If you need a photo of each for comparison I have a populated control panel for each game sitting next to each other in my parts room (not for sale right now though).
There was a person selling $5 Galaga joysticks and control panels, you might check with that seller. You should be able to modify a Galaga harness quite easily.
Here was that post if if helps.
http://forums.arcade-museum.com/showthread.php?t=391490