Conversion to monoshock

I think unless you have some serious additional power to play with, rear tire width beyond 120 is a waste. Even then, fat tires look wierd on old bikes.

Fat tyres won't help the bike handle better, you probably don't need them unless you can get another 20 BHP from your commando engine. I believe that a lot of modern bikes don't need the big tyres they all seem to be fitted with these days. The commando is not a modern bike - it relies on a torquey motor and nimble handling - a different concept, however in many circumstances just as good.

El Japo 250 S/A looks to pansey & weak to me . Liable catastrophic failure .

do a torsion Test . Check out a 850 swing arm . Do a Custom Box section or use Alloy Triumph maybe peraps ,
at least not a Honda 50 one . :x if you expect to survive .