I have now discovered a typesetting firm online who look like exactly the people I need to deal with. They understand the “Sources Chretiennes” layout, with facing Greek and translation. They understand oriental languages. They’re called Atelier Fluxus Virus. So … I have written to them this evening asking how to do business with them. Let’s hope they don’t mind hand-holding me a bit!
I’d been asking around, but not getting very far. Many thanks, tho, to “John” who suggested googling on “Greek typesetting”. That gave me the company above.