G'day again Richard,
can't sleep, too much back pain. Had another look at your post.
A stab in the dark, is the rear sprocket the right one? Could it be a "56-"57 Ariel type? I know they are different, not sure how.
Also, is there a spacer for the inner primary to frame fitted. If it's too thin or not there it will pull the primary outwards and cause the chain to rub.
Cheers