Over the line finally - the method for completing the remaining three letter entries became clear once the given two were located.
Great fun and an interesting linguistic challenge.
That's what I have gitto (although that's almost bound to be the case in a three letter word isnt it?) but I still feel like I have missed the whole point of this puzzle.
SH - that's exactly why I felt doubtful about my solution. I don't think it is a 'spoiler' to say that the fifth word in the endgame could just about be considered an example of the 16-letter entries...
I have all the clued entries apart from 8. I have ?R?IC? and would appreciate a nudge. As to the endgame it is, as yet, a riddle, wrapped in a mystery inside an enigma.