I went crazy in my search for Japanese Namco cabs info and pulled my wallet and bought a Namco Tank Battalion Service Manual from E-bay for the immense amount of €1 (Yes, the shipping from Germany was more expensive...

)
I had been looking on the internet for a Galaxian Namco manual (or even TB) but couldn't find anything, not even at Arc Arc.
The manual that arrived are clearly photo-copies but judging from the color of the paper and the somewhat rusted staples through the stack it was originaly delivered like that BITD (not that uncommon really). Not an issue at all for me, this is still the original thing AND the info in it was what I was after.
So I scanned it and e-mailed it to the Arc Arc guys. It will be added there soon. I also requested for a separate Namco section because Nintendo, Williams, Atari etc. all have their own section but somehow Namco doesn't....
If anyone wants it directly let me know, it's small enough to mail it or maybe Etienne has a small place on his FTP server

Sadly the manual doesn't have any PCB schematics.
It does have the funniest "warnings" section I've ever seen though, containing some cartoon-like drawings. That is actually very smart, because usually everyone skips over the boring warnings section but not this time.
On a personal note I was very satisfied that there were even warnings to not put the machine in the way of an emergency exit or a (manual) Fire alarm point, but that is due to my job of course

Still should have been in every game manual !
Included a couple of the drawings.
I also figured out that the only real difference between the Namco Galaxian edge connector and the Bally-Midway one is the sound-output (like Robin already told me). Of course TB has also up-down controls, but everything else is pretty much the same.
Of course it also has a light output for P1 and P2 which the Bally-Midway obviously lacks.