Wow, what a workout. After about two full days of solving I have a nearly full grid with some ambiguities, the three authors (although at least one of them could plausibly be at least two possible people since I have no quote ideas yet), the play title (which I guessed early on although in practice hasn’t helped me yet), and what I presume to be the four shape words although I’ve no clue how to proceed with them!
I also still haven’t solved 21ac so I’m in the market for nudges there as well as how to proceed with this impressive but impenetrable endgame!