I made a mistake and posted this under EV 1658.
Some answers are given there, courtesy of ProfessorMaisie.
ProfessorM, your 38a hint leads to 4 letter answer, is that correct?
Although "N" appears from a down clue.
I had 3d after I posted but did not know how to parse it. So thanks.
I have answers to 16d, 19d but no idea what letters move.
Yes, hankir - there are a couple of sly twists like that. I think we've discussed Ifor's cruel streak before (and there's a fair bit of the dark side in this puzzle).
I'm still wondering why there's a 'final grid' mentioned in the preamble - that would normally suggest an intermediate stage, but I can't see one!
For blanks you need a total of 4 (they're symmetrical within their rows).
Lewap (if you're still looking) there's a word ladder rising up from the theme word at the bottom to the theme word at the top - change one letter each time.