i have the aga and the ecs version, but if you hold down fire button during loading the game you can select ecs/aga on the aga version in the prefs editor.
years ago on my trusty a500, i had a version of galaga that came on an assassins disk, the music during game was ambient and a realy cool tune...i've searched high and low for that version and cannot find it
i believe both ecs and aga versions are on BTTR if you are still looking for them.