A Norton ~ a Norton ES2 ~ close but not a Commando

My grounding with Nortons.. a 16H and an ES2.

(I am now cured of singles ~ lol)

A good mate of mine however, is endeavouring to define the optimum timing for his ES2.
I have a Classic Mechanics edition which covers an extensive article on the ES2~
Its says ~ 5/8 in fully advanced..

He has three different sets of data for the timing on a 1952 Norton 500cc engine.
1st says 5/8" BTDC
2nd says 3/8" BTDC
3rd says 38* BTDC (which equates to around 3/8")
anyone got a difinitive answer please?

Any innovations on these ~

This particular ES2 that (I believe?) Stuart SS is referring to is fitted with a 16H piston that would appear to be a different compression ratio to the original?