I finally managed to assemble the jigsaw, which has the long entries where I first put them two days ago but I lacked four key answers that would have helped to confirm I was on the right lines. S_pugh's help was very useful, for which many thanks. Even after finishing the grid I had to spend some time identifying some elusive misprints in order to get all of the extract. One has to admire the setter's ingenuity and deviousness with the misprints, but as I said earlier, and Orson comments below, the setter has made few concessions to the solver apart from a few easily spotted anagrams. Even the grid departs from the normal rules regarding unchecked letters, having two entries of seven letters with three unchecked cells each. That's pretty undesirable in a normal puzzle, but in a carte blanche it's bordering on the unacceptable, especially as the ratio of checked to unchecked cells is not exactly generous.
A bit underwhelmed by the theme. Definitely not worth all the hours spent on it, in my opinion, but we all have different expectations of an endgame. If a solver expends all the time and mental energy that this needed, surely the endgame revelation should have a bit of a 'wow' factor.
I don't see why the unclued entry contains the theme, which makes me wonder if I've fallen for some red herrings in my highlighting.