N00b26, glad that little nudge steered you in the right direction. glad you didn't mind me expanding on the seond part of some unclued entries. I knew you didn't mean 'clue' but I like clarity!
N00b26, if it's 39 you're stuck on, one of the elements is longer (letter wise) than the other. The latter, very short, crops up in crosswords quite often.
No, I got 39... It's the second word in 13 that i mean. I see the 5 connected with 20 and the rest were clear also. Pretty sure on checkers so I'm wondering about alternative spelling or ??
If your checkers are just two vowels then the answer is in the Chambers Appendix already referenced, though there’s something fundamentally unsatisfying about finishing a puzzle by simply looking up a list and writing in the only entries which fit. Not very intellectually challenging!