I think I bought a complete (almost) mower from our local recycle, always a good place for such curiosities, I was in a hurry one day and missed a bluish rusty and paint peeling Rotoscythe, but hadn't time to haggle, nor decent vehicle to stow it in, at the time.
I have no recollection of the mower that housed the engine perhaps it was an Allen or similar? I'm guessing now though.
I had several half hearted attempts at getting the engine to fire up, but was unsuccessful, the blade and carrier form part of the flywheel necessary on any engine some folk don't understand, but whether I'd kept and used them I cannot now recollect.
I kept that engine which had an odd governor/carb. linkage mechanism, if I remember correctly, for a couple of decades, I searched for it before lockdown but found only the side start mechanism. I imagine I took that off to help with the non starting and linkage issues, but never replaced it, maybe the spring is broken also, I'll have to ferret it out one day. It's plastic of course, the thin edge of the wedge for both Villiers and all admirers of their more substantial metal only designs of the past.