Well, It's amazing (but also sad) that no one really tried to emulate that beast so far :-(
Did you know that the Galaxian3 hardware is almost the same than the Starblade hardware (see here).
The Galaxian3 hardware is just a pre version of what became the well know 'Namco System 21' hardware.
The Galaxian3 is basically twice the Starblade hardware (once dedicated for left screen, the other to the right screen), with the addition of a specific board called 'V-MIX'...that takes the 3D objects computed by the set of boards 1 (almost the same than Starblade as I said) for the right screen + takes the 3D objects computed by the set of boards 2 for the left screen ... and just mix the result with the video (pre rendered background) signals coming from the laser disc players...
I'm sure 80% of the job is already done. Argh... that would be the ultimate challenge for this non emulated laser disc game! And we are talking about a great NAMCO game that many of us would like to play, not an obscure and unknown game...
I'm ready to provide anything you need, do all the test required, to commission/kickstarter/whatever to make this happens... it's still time : my galaxian3 is still 100% up & running, including both mission : Project Dragoon & Attack of the Zolgear :-)
Once again, don't be afraid about the size of the game, it's just 'twice' the Starblade hardware (2 CPU communicating) + pre-rendered video on the background...
Saving Galaxian3, guys!