Just left with the one, and maybe I have a letter wrong, because I can't see a word to fit. It's relating to 9 Across, for which the clue is:-
"What's dropped letters of nearly two ounces outside post office." (8)
I have L-R-G-A- towards it.
Many thanks, Malone. I thought I'd put a wrong letter in, and that was the case! I took the horse going down to be RACER, but it's obviously PACER. "PR" for pair, and NOT "RR" which I took to be the pair!