What good news that Mr Magoo is appearing as a Spectator setter. He's this year's Times crossword competition winner isn't he - and brilliant. Fine crossword, too!
Fun puzzle - certainly the title was helpful, but a bit of whimsy in January goes down well! Slightly unhappy about one of the unlighted squares in 14ac which could lead to three different letters all making words that mean the same thing. Also can't see the wordplay why or wherefore in 35 dn. Vague pointers would be welcome.
for 14a, I opted for an S since to prise means to lift with a lever. Like you I mulled this one over for a while. To my mind the other choices did not fit in well with "leverage".
35, there were only two words that consisted of only Roman numerals that would fit (I think). I went with CIVIC, with the possibly weak reasoning that civic and roman both mean "related to a city" - a very specific city, in one case.
Thank you, dr b. Your reasoning has gone very much along the lines of ours. A little irritating that they can't both be completely tied down. Annoyingly the z, s and c versions of 14a can all be found in the current Chambers for both definitions.