I don't know, looks more like a Royal Enfield 250 Crusader to me.
Later on, Bill
Most of it looks Royal Enfield ( frame, wheels, etc) but the Crusader motor had a RE inside a bulge at top front (I've had 5 or 6 of them, got service manual 'safe' somewhere
) ( I see a picture was posted)
It may be a motor for export market?
The clutch side would have given it away as the timing gears meant that side couldn't be modified the same as right side or its a really early motor in later frame?
Doh, didn't read all the posts.
The 'cooling' disks on front wheel were stock on Super 5's and Continental, Continental GT.
Was probably the only genuine 100mph British 250 made ( Ariel Leader/Arrow could be made faster but needed a bunch of work, one was timed at 126mph in 1966)
It was a very successful trails bike (I think either one of the Lampkins or Mick Andrews won British championship around 1970 on one)
PJ