Well the mega thread has to die...
IT'S BLOODY WORKING!!!
Nino was on the money with the score reel switches.
Once I figured out how they are supposed to be set. (They well all originally set slightly differently!).
There was a wiring problem with the 100's reel zero switch being wired to the carry-over switch, which had me stuffed as I was just setting switches visually...
Once I got serious and looked for continuity from the ball count unit - across all the zero switches - I found the smoking gun...
Nice being able to play a few games with the glass on for a change! Makes it much quieter too!
Now for all the little crappy things like buzzing coils and dirty globe holders etc. etc...