Not too sure about what the cabinet was in a past life, but it looks to me like the monitor was modified at some point. Look how far recessed it is from the monitor glass. I can't realistically see a manufacturer purposely building a cab like that. It could be a homebrew cabinet as well. I have one that is a completely hacked Galaga. Bootlegged board, cabinet, everything.
As far as I understand it, a guy used to build Ms. Pacs and Galagas way back when in his garage (1982 or so). Then he'd put them on his truck, and run around to all the local operators. When a dedicated Ms. Pac or Galaga was $2500 back then, he'd sell you "his" Galaga or Ms. Pac for $1500, or both machines for $2500. Game plays identical, so why not? Long and short of it, this one survived the years, and actually still works. I think it even has a manual too. Unfortunately, I don't think the guy survived without some jail time, once Midway got word of this going on. (Not sure on that one, though)
So, the point of this story is that it could be a "bootleg" cabinet with a Midway door (I think my Galaga has a Midway door on it, Galaxian-style). Just a thought.