Hi
You need more detail, from what I can see the head appears to be DOHC (1951), that is only going by the photo that appears to show the inlet cam cap behind the fuel tap and tank fitting?
The thing I would be concerned about is the barrel, something seems wrong as there appears to be a substantial spacer between the case and the barrel, is it a 600cc side car engine?
One guy I know of has a genuine 600cc sidecar engine here close by in Aus, but I haven't set eyes on the engine yet.
There seems to be enough fins for a 30M, although I have been told by the old timers that this also, is not a real guide as Norton at times grabbed whatever they had close by to fill orders, i.e. they modified to suit.
Frame wise the featherbed 1951 didn't arrive for the privateer until March 1951(ref Roy Bacon Norton Singles), and I wouldn't be surprised that a few garden gates made it though in this time.
End of the day up to you, as when I brought my 1955 short stroke Manx in 1971 it really was in a sad state with Dominator tank etc. only good thing is I only paid $370 au, had to borrow $100 deposit from the mates and paid it off over 12 months. Luckily for me it has all original engine numbers frame numbers, gearbox etc.
Best of luck with the decision and if I had the money I would be very inclined to buy it as there is a hell off a lot to start with.
Burgs
