I have scanned more of my English Mark Dart 6000 series and Galaxy series manuals & schematics.
The 6000 series equipped with the "Super Spider" target head must use game eprom chip U15 with version 3.0 or later.
The manual for the Galaxy dart game posted on Arachnid's site is for the Galaxy Darts equipped with a switching power supply. I have scanned the Galaxy manual with the linear (analog) power supply. This is the one with the tranformer, filter capacitor, and circuit board that looks like the 6000 series power supply.