All done and in the mail;
pace Dsc, once the PDM came I found the internet very helpful indeed, even though I'm one of those with no great knowledge of, or interest in, the subject, beyond an uncomprehending fascination contemplating those minds, like Drxx, who evidently have diagrams of countless such situations going back centuries, and instantly recognisable, in their heads - and who also evidently find it hard and distressing to comprehend that we lesser beings might not be able to do this - or even care to...
Another such genius is evidently Crash, to whom thanks for a staggeringly intricate construction - my initial annoyance with the weirdness of the clueing was almost completely transformed to admiration when the the multi-layered intricacy of the thematic requirements were revealed -
'almost', because I'm still foxed by the parsing of quite a few clues - in particular 21a, 22a, 37a, 33d, and 35d. If anyone can devise a means of explaining these without giving TMA I'd be grateful to be relieved of the mindworms still gnawing away - particularly the one with the pink prow - but if not, it doesn't really matter.
Well done, WS!