I have to agree as I also cant find anything on any Villiers called a 250R or R250. I also at this stage have my doubts its a 250 as it does look a bit small to me.
I dont think its a Monet Goyon engine though (did they even do there own engine?) I have some time ago joined the French MG owners site and even though its quite hard as I do not speak French they have confirmed its not the right engine for the frame. The frame is a S17. They were also unsure of what the engine was
On the gearbox, this may well be a MG one if they built there own. Have not really looked into that. The foot change was not factory as this is a rocker type foot pedal welded to the end of the gear change shaft with the hand change bolted through the shaft. Obviously done years ago but can see no reason why. Had to remove this to strip down the gearbox and will probably not reweld it back on. With it the box it will not work with a kick start fitted. I fitted kick start on but all became far to crowded to opperate anything. All very strange and can see why the seller said the bike was push started, though cant see a benifit of having both.
I am also struggling to ID the magneto, looked at loads of online photos and cant find one like this
. This is the oldest bike I have had and my first non British, bought it because I liked the look and the patina but nest time I will stick with British