Thanks for the pointers. Ludicrously, by the time I checked back here to find them, I did indeed crack it. I really had been unsuccessfully bashing away at this all week and then as soon as I say so, it stats to fall into place…
... think one of those that you can only confirm in chambers by looking up the tradititional spelling ... having completed ok think I have a 'blind' spot, for probably clever word play for 13A ... or 60 herein ...
To explain ... I took the first word as the answer (a verified synonym) ... then wordplay 1 letter 'about' + 1 letter 'fifty' ... leaving 3 letters for 'or 60 herein' making no sense ... Unlike me to stick to first conclusions! ... Doh