I'm stuck on the endgame but have the full grid and the missing letters.
So I guess it's not important, but I just can't figure out the wordplay for 4d and 31d.
Best I can do for 31d is a very, very abstract (and medically inaccurate) description of an organ.
And for 4d the only thing I can think of is a French town. But can't see how that would fit in.