space pinball is the prototype for galactic pinball. its really fun. the tables are different than the retail release. i haven’t played mine for awhile, i recall some things like the highscore was never coded.
Unfortunately, you’re not going to get a lot of answers to these questions, because no one really knows the full answer for certain. There are a lot of rumors floating around about these games, and not a lot of facts to back them up.
All we really know is that there are probably still prototype carts out there, since they were briefly demoed at shows, but whoever’s ended up with them isn’t talking. Even if they were, it’s unclear how far along in development they were – they’re likely unfinished, whereas Bound High! was close to completion at the time it was canceled. Dragon Hopper is probably further along than Zero Racers, just based on the comparative amount of information we have about both.