Wendy, thanks. Also thought of Trend yet makes no sense to me either.
These are my answers around it- just to make sure have right letters.
51 a) Scintillate(5) Glint
The last letter of 51a is first letter of 52 Down
57 A) Cut of beef(7) Topside ( last letter E = 3rd letter of 52 down)
64A) Reigned(5) Ruled( d is last letter of 52 down)
Thanks all, Christopher