I was digging through some old albums of my dad and I found this excellent picture of him scrambling on a Matchless motorbike. Does anyone know what it is?

My dad scrambling on an unknown bike

My dad scrambling on an unknown bike

It looks like a 500cc bike, but I could be wrong. The engine shape is pretty distinctive, so I’d imagine someone out there will know what it is.

It might be a G85 or a G50, but the exhaust loops around to the wrong side, but my Dad may have modified it. He was pretty handy in the workshop which you can read about here.

So can anyone out there on the internet solve this mystery?