Still puzzled

I've got a puzzler here and am reaching out to the old timers and obsessive Norton Owners.

I purchased an atlas barn find with some really odd engine and gearbox numbers.
engine - D6 - 7713
gearbox - NA 1938

With some minor research the best I can figure is this bike may have been bobbed in the late 60s or 70s.
Additional recent findings trace the bike possibly back to San Francisco.
Does anyone know of any British Bike Shops in San Francisco open in the 60s or 70s that would have restamped their rebuilt engines or gearboxes.
The engine is not typical. It looks like it was built for speed. It has a lot of period correct performance parts on and in it.

Thanks for your help!

We've seen this asked here before before and before
You don't acknowledge replies ?

Until you post a pic, and unless someone can identify it, will remain unknown who restamped that oddball engine number.
Perhaps it was stolen ?
Gearbox number seems to fit, NOC could probably attach it to a particular bike.

Rohan - I'm having problems getting my photos to post. Can I email them to you?

You have to post them to a photobucket or similar account.
And then post the links here, using the button.
Cheers.

You want the img code when you get everything on Photobucket. In the meantime, I'll pm you my email and you can send them to me to post for ya.

Cheers

Colorado's Atlas pics...

Looks like its definitely an Atlas.
Hard to say whats happened with that engine number.
That last digit is a 3.

Bit of a long shot, but the magneto will have a little tag on it that gives a date code.
The Amals will also have numbers stamped into them, that change with the year.
Could have been changed at anytime in its life, of course.
But may give a clue to the year - early rather than later 60s.

Any owner could have done all of that over the years - after a crash even.
Its all just bolt-on stuff or hacksaw stuff , except for the alloy rims.
Cafe racer was a popular look for Nortons.