Only time the names Wrench and Mr. Numbers were mentioned was by Fargo guy (season 01 episode 06) and he said that two assets named Wrench and Mr. Numbers were sent for him but does not specify which one was which. May be off camera the guy told Malvo that the deaf one was Wrench but I don't think it was ever clarified to the audience, or was it?
So how does the audience know that the deaf guy is supposed to be Wrench and other one Mr. Numbers?