Hi Millzy,
I thought I spotted that in the background of the photo of the Centenary. This is an Atco Deluxe. It looks like it may be one of the middleweight series. Can you put up a photo of the whole mower front on? Under the main chain case (the large one) there may be a brass tag on the chain case bolt. Have a look at to see if there is one there and let us know what the plate says.
Cheers,
Sir Chook