I agree with Janephilip - this one's not easy and the answeres I have got fail, in many cases, to convince me.
I'm still stuck on sixteen or so - help with these cited below might kick what is left of my brain into getting the remainder.
33D - I'd upset unhappy Head with mark : E minus! (12)
?????V?N?A?? [DISADVANTAGE comes to mind but doesn't seedm to make any kind of sense]
43A - Cardinals travelling around the Aleutians, say (6, 3)
????N? A?C
43D - Vulgar account - putting book down, embarrassed (3-4)
???-????
57A - Musician requiring length of old ringtone to be unlimited (9)
????N????
41A Setter does rock for an audience; Eagles, for example (4, 6)
M??? ??T?R?
As usual, i wouldn't necessarily defend the veracity of some, if not all, of these letters.