Thanks Brendan—I had all of that except my “twice” was two letters which ALMOST worked!
Big PDM moment for me was a suspicion about the inner ring, closely followed by the ring entry that is defined, which reinforced each other and led to being able to fill out all of the missing letters—everything quickly fell into place then. Very amused by the degree to which Chambers was adhered to at a key moment, felt like a bit of a cheeky comment on how one must solve Listener puzzles!