'Take your hand out of my pocket, thief!'

Okay, this one is driving me nuts. In a scene just about 20 minutes in, Sidney Falco bumps into an angry client named Jimmy Weldon with his girlfriend Joan outside the Twenty-One club (where J.J. is dining), and the client berates Sidney for not getting him enough press. It is he, not Steve (Martin Milner) as credited here at the imdb, who says, "It's a dirty job but I pay clean money for it!", as well as the line that is the subject line of this post.

The characters of Weldon or Joan are not credited on this page, at least not under those character names. Since 3/4 of the supporting cast receives no onscreen credits, I suppose most have been duly noted by people familiar with their faces. Does anyone know who the actors are, so these details can be corrected?