And FINISHED! With a few more clues from a third perusal of this forum (including the 4 crossers of the Spooner: bit of a cheat but then the answer is pure American, so feel justified!).
LoI: 27
Stil can't parse 13d, though our answer fits 5 crossers and meets definition. Husband had an earlier idea starting with H which fitted but would have left 18a ending in A, which looked unlikely! Got 16d from 2 crossers and CrosswordSolver, then 18a and thence 13d.
Amazed to have finished, given that the whole lower half was empty a few hours ago. Thanks for various hints from various folk.
And in a few hours, next week's challenge: a little easier, I hope.