I do not know if those early bikes came with the little hand books that came with the later models, they most likely had something. The BMS 'The GOLD STAR Book" by Bruce Main-Smith Publication has a maintenance section and complete parts pages for early and late models. The book was available from Prew in the UK and I would encourage you to get one.
While most of the info in the BMS book will apply to the ZB bikes there are a few things not covered for the pre-swing arm setups.
What you need are the early factory Service Sheets that covered individual topics like plunger suspension and early gearbox. These can usually be found free online but I do not have the links handy.
If you pm me with what you need I will see if I have them to can scan for you.
PS I just typed in BSA Service Sheets and found multiple sources for the data.
All BSA's came with an owners handbook from 1910 on ( nothing available for the Minerva engined BSA )
In fact the deluxe ones came wih a hardcover diary with space for payment stamps and sll sorts of things like UK road gradients UK light up times etc etc
These were compiled into a single volume titled "The Book of the BSA" along with brief model descriptions.
Post WWII then became type specific "The book of the BSA Singles", " the book of the BSA Twins" etc .
ZB's would be covered in Volume 12 or in the singles book credited to Mr Munroe The BSA OC NZ
have the 46-55 B series handbook as a pdf download MC 618 previously mentioned by Magneto Man