I haven't finished this enjoyable puzzle but have got far enough to answer 76D.
'Old railway car - it's cold (4)'
A neat and tidy wordplay, and the answer is in Chamber's.
But I just wonder whether the solution is properly upright and reputable, being an interjection without - arguably - etymological pedigree.
Maybe I'm being precious, but as a newbie solver I just wondered whether anyone else raises an eyebrow over this?
Malone, for example, our doyenne, I'd be interested in your perspective...