19d Curt historian picked up peaceful woman - a real pickup (7) ?IV?NER. Livener? (historian Levi, but whence the REN?).. Diviner? (DI, peaceful woman?).....
And 20a Conjecture informally about fare? (4) CEP?. 'Cept? (except), but don't get the word-play!
That makes sense now, K! - Many thanks, and thanks to you all! I hate to get to the end of struggling with the Mephisto and be unsure of the last one or two letters!!