Regarding the Uranowitz and Swenson switching roles comments, in the script, Czolgosz says to Emma Goldman that he is 27 (or thereabouts). That line can be cut (or the audience can suspend their disbelief), but if they are trying to cast these real-life characters semi-realistically, Uranowitz is a better choice (even if the role calls for a bass-baritone..). Having seen clips of Swenson doing Berger and The Pirate King, I'm sure he can pull off Guiteau, even if he's rather too good looking for it.
But yeah...I am in love with Judy Kuhn, but she looks nothing like Sarah Jane Moore (maybe they'll put her in a fat suit?), and playing a brash comedic character will probably a bit of a stretch for her, but I'm sure she'll do fine regardless.