I've got a Galaxian machine that I've been hacking on. So far, it runs 9 different games: Galaxian, 2 versions of Super Galaxian, 2 versions of Moon Cresta, War of the Bugs, Galaxian Part X, Scramble and Pisces. I've got several more ROM images to get going, as well. This page will detail the modifications that I've made to this machine.
Scott Tunstall is disassembling Galaxian's code. Keep checking for updates.
Patch to make Super Galaxian work