After some serious agonising I now have a full grid. I do however have some problems
1. There are two possible answers for 8d (I of course had the wrong one for a long time) - this seems incongruous for a listener clue unless it is deliberately intended to mislead
2. I'm assuming the 3rd letter of 20a is S, but am struggling to verify as the answer without it refers to both the singular and plural
3. I have the intersection at 33a/29d as unchecked, providing the same extra letter for both entries - which you could argue means that it is checked
4. I haven't a clue (yet) as to what the two instructions are meant to mean.
Other than that, everything seems to work out nicely.