I confirm letter I for 7mR class of the international metric rule. In this rule letter A was for large schooners and letter B was for 23mR class and so and so.
Now about Herreshoff universal rule I think letters A to G were for schooners and ketchs, letter I for 150 ft class, letter J for 120 ft class then down to letter S for 18 ft (basically a one design).
Probably a 40 ft universal rule boat would be a R-boats like n°R1 SIR TOM ?
I did not get the opportunity to know about n°5 and n°6. Maybe Adam knows?
Well ... I have a question for specialists:
In USA you say LOS (lenght over spars), we say LOA (lenght over all) = from front of bowsprit to end of the boom.
You say LOA (lenght over all), we say LOD (lenght on deck) = hull lenght at deck level
We all say LWL (lenght water line).
Is this correct Steve, Adam?
Regards all