Bill, thank you very much for taking the time to answer, and for providing the pages you attached. I realise it's not a simple thing to do, and would be made doubly so by the fact that the text in question is not of ancient origin, but written in 1913 by Aleister Crowley. I refer to what is known in 'magical' circles as The Star Ruby, a ritual for the banishment of evil spirits and (possibly) the calling of Pan.
As I am aware, Crowley made some grammatical errors in his writing of the text, perhaps purposely so, but not being a Greek linguist I cannot clarify this. My reason for the Koine pronunciation is that Crowley was a student of 'Athenian' Greek, and references to teletarches, iynges, and synoches in the text are concerned with the Chaldean Oracles which, as I am aware, date from the Koine period. If 'Athenian' Greek were another option for pronunciation, that would also be fine.
If this makes things (even more!!) difficult, then I can stick with what I know, and many thanks again for taking the time to respond. If, however, you would be interested to have a look then I can post Crowley's Greek, the English translations, and the phonetics I have, to see what you think.
Again, my thanks Bill.
Craig.