Where is the rhyming connection here?
Good question, it would be hidden. You'd ask a guy wtf "Lady Godiva" meant and he'd say "Fivah". The animals for numbers, I don't remember. Possibly some connection ages ago that you similarly needed to have the story for.
Ah, I incorrectly inferred that you were involved in the creation of the slang.
It is London slang, but it isn't necessarily Rhyming slang. In fact, these terms are generally understood to have originated as racing/bookmakers' slang, and go back to at least the end of the 18th century. This is a 19th century slang dictionary.
* https://archive.org/details/slangdictionarye00hottuoft/page/...
At first I was skeptical and assumed that you had not realized the parent comment to which I had replied. But I checked and was still skeptical when I checked 'monkey' but indeed there was an alternate definition that was numerical. However I can't find one for 'donkey'. But maybe the parent's memory is faulty or more recent slang has added these numerical denotations in a greater context than just the parent's past workplace.
Re:Cockney Rhyming Slang History
by 082349872349872 on Wednesday October 14, 2020 @05:49AM
(#24774867)
One of those lemmata casts doubt on the veracity of "Port Out, Starboard Home." I also enjoyed the dual meanings of pot-walloper, similar to "cutting coupons" shifting semantics at opposite ends of the NRS social grades.
A fair few of the guys trading derivatives when I started were "locals" is two senses of the word: they were from London and they they traded as market makers.
You'd have special words for numbers like donkey and monkey. Combined with general market terms you'd say things like "I'll lift you for a donkey", IIRC meaning I'll buy 250 of those contacts.