Thank you. Well, I assume it begins with D but haven't parsed 27A to confirm. I saw the definition in the thread but couldn't think of anything - will keep trying.
In the message, I have the first 12 letters (I think). All my clashes are in the top half of the grid so the remaining 4 must be overlong answers, of which I haven't yet solved 41A or 46A. There is an N in the last overlong answer ('shrubs') but I can't see how it can be in an unchecked cell (ie not interfering with the down clues).
I'm not planning on submitting my solution as I've needed help, I just want to see what the endgame is as others have praised it!