Could be a Space Invaders Deluxe/Space Invaders II. It has the rounded edges and a weird, shallow control panel. Control-wise, I think it uses the same swiveling lever as Galaxian. The rounded corners are constructed differently on SI than on Pac-Man and Galaxian. It also has a very different colored laminate than the other cocktails. Below are a couple pics. The first is from KLOV, the rest are pics I took through the window of a local operator's showroom. The SI is sitting right next to a Pac-Man cocktail. I was thinking about building a cocktail and took these as reference photos as to the differences between them. AFAIK, SI was the only Midway cocktail where the back panel is built like this.
A Rally-X should be pretty easy to spot since it had a horizontally-mounted monitor--a rarity among all of the Midway cocktails.
Does yours have the 1-slot coin door?