Found it. ARGHH!
I must have read about half of the workshop manual tonight looking for a clue, then just as I close the book and go to put it away I see it staring me in the face on the cutaway motor on the front cover lol.
The number is 23 7W G150
22
I'm 99% sure on the 7 but the top of it's stamped right along one of the sort of "serrated" ridges on the number pad. It could be a TW instead of 7W? But as i said 99% it's a 7.
Now, fingers crossed I can be the one to provide this beast with a new home.
