Hi Peter
The mounting plate holes on mine were over-size but in the right place. My modification came from a mistake on my part - overtightening a bolt and shearing off the head, then I couldn't get the rest of the bolt out. Oops! I welded a new plate on the back of the existing mount and it seemed to work ok.
I used M8 bolts.
Is your mounting plate big enough to drill another hole in the right place?
Do you want me to put up a closer pic?
By the way, good luck with your wiring - I got as far as trying to turn over the starter motor yesterday without success
reckon its to do with the immobiliser.
Cheers
Tim