Hi Arty and Beech,
Arty, the parts books are a stapled booklet and can be hard to source as they have been out of print for many years - they do turn up though from time to time. Will do some searching.
The rollers for the Atco light mowers are relatively straight forward, however, the earlier models have a well engineered but more intricate setup. I certainly would take your time and take photos as Beech said as this helps to reduce the potential for confusion during reassembly.
Parts for these mowers can be hard to source here in Australia. That being said, most of the spares that tend to be needed are consumable items such as bearings, rings, coils etc. Sometimes these can be sourced here from a couple of places but otherwise they can be obtained from the UK. Heavy spares are a bit harder but can be found provided that one has a bit of patience.
In terms of the engine on the 1948 mower, I can assure you that this type of Villiers 2 stroke engine is original to the mower. In the late 1940's up to the early 1950's the 17", 20", 28" & 34" mowers shared the same frame design. Other than the cutting width, the only main difference was the 17" & 20" were powered by the Villiers 147cc 2 stroke and the other two were powered by a 350cc J.A.P. With the introduction of the light mower, the earlier 17" and 20" mowers were replaced by a light version. In about 1957, Atco decided to start making a 4 stroke version of the light mowers which used the same frame as the light mower but had flat bar spreaders and a Villiers Mk 7 engine as well as a heavier version with angle bar spreaders and a Villiers Mk 12 engine (both engines were kick start).
Kind regards,
Sir Chook