Charlie Moore (aka charlie)

Richard, can you find the engine number, usually stamped into the cowling. This will help identify model etc and help find the correct set up.

Looks like some sort of scaper.
Might be worth contacting the Tool and Trades History Society (TATHS)

Filler plug arrowed in photo below. Recommended oils, Castrol XXL, BP Energol SAE 40, note these are engine oils not gear oils.

Another possibility is that the mower is not a Barford attachment but a modified Merry Tiller or other make. I don’t recall seeing a rotary mower in any Barford leaflets.

If you want a manual for the ‘motor’ I assume you mean the engine, then you are looking for a Villiers Mk10 engine manual. If you want a manual for the machine it is a Colwood B. Dashwood Engineering were the makers.

Looking at the handlebar and trailer arrangement I would say that is a home made modification. As far as I am aware a trailer was not an option for the Colwood.

Copy uploaded to website

My copy has just arrived.

I would say stick with the original design,

June issue is now with the printers.

Torque settings were not published for most small engines eg JAP, Villiers etc. The question has been asked before and no information has been found.

Another problem may be trying to go too deep in one pass, eg full depth at first attempt.

There is a trader that gets around the vintage shows who in addition to selling new tools also sells good quality old spanners. He has a very good knowledge of the older stuff. If I see him and can remember to ask I will.
I wonder if it would be worth asking the Tool and Trades History Society (TATHS)

Online copy of April issue uploaded to website.

My copy has just arrived today.

I think that will be a Mayfield 10, the Museum of English Rural Life at Reading have the factory records and should be able to date the machine from its serial number.
For equivalent tyre size there are a number of online conversion calculators

It looks very much like the type of universal joint that would be used with a 1/2″ socket. I found something similar on the RS website

I doubt you will be able to buy a new one, the only option is a second hand one off another machine with a similar fuel cap.