Any info on the owner of that game? That may have been one of the others I've been looking for but I'd have to chase it down to be sure, mine is also a graft between EM and solid state. It is digital, has memory and a sound card but no attract mode. The solid state portion is driven by EM technology. Unfortunately, there is a lot of alkaline damage to the one of a kind CPU board so I don't know if it can be rescued.
The story I heard when I bought mine was that Gottlieb was looking for someone to make their boards for them since they were new to solid state (GTB thought solid state was a fad or something). So they pulled a few Solar City's off the line and took them to several different board makers. It was like, "here's an EM pinball, make it solid state", then they picked the best company design that fit their needs.
Mine is one of those games, actually, it's one of the loser games that wasn't selected. The cool part is that I found a business card inside my game from the company that made the boards. I figure there must be a Rockwell System 1 Solar City test version out there somewhere but it hasn't turned up yet (just like the System 80 Hulk and System 2 Black Hole 7 digit game that have turned up lately). I keep looking.
Steve