Space Invaders was a vertical monitor.. but the awesome projection on the background made it look like a wide playfield Taito Space invaders cabinets were so prevalent back then where I come from, that they were the first machines (at least in the very beginning) Ops used to hack out another game in them.. e.g. "Alpine Ski" in a SI cab is another vivid memory.
I know what you mean about the mirror... As to how they got rid of it (or did they use it) I don't remember. this was over 30 years ago when I was only 12 or so, but they did it allright. A lot of times the bezels painted black as well which was another sad thing.
I honestly don't ever recall seeing a converted black and white game. I "think" the first conversion I encountered was a Williams' cab - thinking it was Defender.