Having looked again, I found some little squiggly numbers on the plan on Page 28 of the Hundleby-Strasheim book published in 1990 and in 1:6th scale, the tracks are 86.6mm wide.
For those who looked, saw that the dimentions were there and thought "Dimwit"! I appreciate you looking.
I have ordered the new book and hope to find loads more information on the beastie.
