Hi Millzy,
Did you manage to find the brass tag under the chain case? With respect to the date of the mower, it is later than 1935 as in 1935 the kickstart was only fitted to the 14" model and was not a pendant style. Given the engine type (which looks like the SZ prefixed Villiers), the handlebar configuration and a few other clues it would appear to be at the earliest 1937. It should be noted that there were some prewar models produced postwar for a short time. Atco's first shipment to Australia was in early 1946.
It also looks like the catcher that you had on the Centenary is actually an Atco catcher for a Deluxe model - not sure if it is the one for this mower but it would be close. The bolts in the catcher body should fit in the slots in the mower body.
Cheers,
Sir Chook
