Your game is one of the 12-15 Space Station prototypes. The 'X' in the serial number is Williams destination for a prototype game. Usually Williams will make around 12-15 proto's and then run a batch of 100-300 sample games to market test a game before running a complete production run. Games like Starlight or Varkon only made it to the proto/sample run and therefore never got made into a production run. Your game is definitely a PROTO-TYPE game. The sample games do not have a 'X' in the serial number.

Sometimes the prototypes vary slightly from game to game since they are hand built in the engineering lab, where-as the sample games are built on the production line. Sometimes the proto's use left over cabinets from the games before them (like Williams's Fire) so the holes on the cabinet might be a feature from that previously produced game. The hole cut out on the head might be the same as one of the beacon lamp domes from a F14 pin.

Your game is a proto and most likely will have the black mini-playfield unless someone switched it to the production one.