Yes, I hope the info I've provided is useful.
Looking again at the photos I took, I began to wonder whether the double-choke I mentioned was in shunt (across) with the AB terminals, rather than spurring off as series chokes. A shunt arrangement would mean that it'd be a transformer of a kind. But after then re-checking my Mk3 faceplate with an ohmmeter I was able to confirm that it's definitely not a shunt inclusion. Indeed, if it were, the choke(s) would rapidly burn out as soon as the 45 - 50v DC appears on the dropline AB terminals for the phone (the chokes are made from very fine-gauge wire).
Here's another practical issue to consider. For anyone thinking of acquiring a Mk3 plate to use and who might already be using an earlier issue NTE5 with brass threaded fixings (I mean the outer pair of holes, not the inner pair) do take care to obtain the correct machine screws. Suppliers of the plate often provide a set of screws - some self-tappers, others threaded - but invariably supply the wrong size, for the threaded ones. What you'll need instead are a pair of M3 x 35mm long machine screws, either countersunk head or cheesehead. The 35mm includes the head of the screw. These can be bought quite cheaply from various suppliers on Amazon, if necessary. If you don't have the correct length of machine screws you won't be able to hold all three faceplate components together. The NTE5 main body of course is normally fixed to the surface-mount or flush backbox with a short pair of M3.5s (not M3s), using the inner pair of holes. If you don't happen to have threaded inserts as the outer fixdowns of the NTE5 ensemble, really your only option is to use the self-tappers but, if you do that, in time the fixdown may well loosen and then fail to keep all three sections together. And if you're especially unlucky you might even crack the surrounding plastic. If you force the self-tappers into the threaded inserts, the fixdown is kinda ruined for good. So I'd advise that you avoid all of that; if you've threaded inserts get the correct screws. I've always felt it was a bad move when Openreach stopped using the brass threaded inserts, and in fact in other respects the general quality of all these components has, in my view, dropped quite noticeably in recent years. The same sort of care re screws would need to be taken if instead you choose to use a Clarity or an ADSL Nation faceplate. Clarity seems to have stopped trading but they used to make a specific point of supplying correct screws for their faceplate. The Clarity faceplate is, I believe, still available from Solwise.