I remember seeing a similar one at Honiton Hill Rally some years ago, possibly the same one? It may have been made by another company that preceded the Easi Mow design.
Is there any evidence around frame of machine where engine mounts to suggest it had something different previously? Aspera may have been a later option. Yes it should be possible to turn engine by hand with plug in, you should feel it become harder at some point as piston comes up on compression stroke. If engine has been stood for a long period one of the valves could be stuck open which would cause loss of compression.
John, welcome to the forum. Unfortunately I cannot help with date. To refurbish or just service very much depends on what you intend doing with it and what condition it is in. If anything mechanical or electrical (ignition) needs replacing or repairing that would be first priority. To give it a full restoration and paint job is personal preference.
Clutch and throttle cables can be made up. I have made several in the past, cable inner and outer along with suitable nipples can be bought from motorcycle parts suppliers eg trialsbits If you know the dimensions John Cruse at the Mower Centre will probably be able to make them for you.
Jim that is sad news. A huge thank you to Karen, yourself and everyone else that helped put these events on.
On a different subject would like a copy of the price list in photo below?
I think it could have been a motorcycle engine, not aware of what other machines they were used in. Meetens are a good source of Villiers parts although I dont know if they would have parts for this model.