It would have been helpful to give what letters you have, as I've already sent off my completed grid.
The eighth word though is of four letters, which can be split up into two complonents. The second is the same in all cases, and the first is of similar types. I hope that this helps.
I do not have a frame of reference for 55 but it must relate to either of the last two words in the line of the carol.
Hi ulysses100. I see from the correction published in the latest Spectator that the unclued 105 was not 'spare' but a member of one of the sets. For those of us who cunningly settled on 'spare' this will have cost us dear, not contributed to a sonny disposition, cut the heart out of our cheer, and so on....