Thanks for replies.
I’ve looked closely at the frame number and I think it could be more likely W87315. Is there any info available for this number please?
The digit "7" Norton used had a curved vertical line. I do not see that in this case.
Having about 170 pictures of Norton frame numbers and nearly 300 engine numbers I think have sufficient reference to stick to my previous statement.
I therefore stay with my previous information.
There is not much more to tell.