Thanks much for the helpful replies, all. After a couple hours of often very slow progress, I've just solved the puzzle. I'm sure the endgame was less extraordinary to those of you who tackle the Listener often, but for me, having never solved a puzzle like this, I found it almost revelatory. I spent a while not really sure how to progress with the final word, then when I stumbled upon the solution, I couldn't believe it all worked. What an amazing feat of setting.
I must admit that, sadly, there is still a single cell that remains unfilled on my grid because I cannot disambiguate it between two possibilities. There was also a good handful of answers for whom the missing letter had to be back-filled via the quotation.
If someone would like to give me any nudges as to 13a, to help me fill that last cell, I would be very appreciative!