Identifying older Norton head?

The underside of head says '23166'. On the top of head above intake rocker box cover there is a raised letter 'U'. I couldn't find any other markings.

My gut instinct tells me this is from an Atlas, but I'm not sure. Does anyone know off-hand based on the information I've given?

I can get some pictures, but I don't have any at this particular point in time.

I've been saying that this head will fit the late (1968) Atlas P11 bottom end I picked up, but I want to make sure..I'd hate to be misleading anyone..

Thanks,
-Jordan

ludwig said:

http://atlanticgreen.com/nhth.htm

Click to expand...

So it would appear that I was correct in saying it's an Atlas head and should therefore fit the Atlas bottom end. Good deal.

-Jordan