Hi Jarrad,
Sounds like a good score there. Like all classic machines they are collectable. However collectable and valuable do not always go together. It really depends on the model, condition and what someone is willing to pay. I have a few Atco mowers and generally the ones that I have bought that date from the 1950's and 1960's cost me about $40 each. I have seen a few fetch $100 or so on eBay but again it depends on model and condition.
Dating Atco mowers can be tricky but machines built between 1947 and about 1964 often have brass size/year plates on the right side. 1454 would denote a 14" cut machine built in 1954. Where there is no tag there are other methods of dating them but these are not as accurate. If you need further assistance put some photos up I can give you an idea of the approximate year of manufacture.
Cheers,
Sir_Chook
