Finally got there with a massive PDM once I identified that pesky 5th word!! I spent hours searching for new words of the wrong length, but it all works very neatly in the end.
Greengage. The last letter of churn (winding it up) in a four letter word for deserts.
It is an & lit. clue. A rare example of this type of clue that actually works well.
Still working on the last stage, but in terms of clues I don't understand the wordplay for 37a or the significance of 'thane' in 16 - my answer seems to be Indian?