"O" on the rings means "This side up" and the "40" probably does mean .040 over. Do you have a shop that can measure them?

326 rings are very hard to find due to the strange size.

TOHCan rebuilt a 326 recently and was able to find rings that could be made to work. I know I should know this but I just can't seem to get a grip on my memory of the event.

By the way, I visit the UK several times a year. If you have a need for small things that are not urgently needed, I can get them to you easily. I also ship to my company in Exeter all the time and they are used to seeing packets within the packages that need to be forwarded within the UK.