I've seen films with similar plots to "Get That Man". And, the film is occasionally a bit too complex and difficult to believe. However, it's also incredibly well made and engaging and I recommend you see it.
Wallace Ford plays Jack, a guy you have to feel sorry for as well as like. He's accused of a crime he didn't commit and a shyster lawyer (are there any other kind?) sees him in a police lineup and realizes he can make a killing. It seems the heir to a fortune looks exactly like Jack and the lawyers knows that Jack can pretend to be the heir, John Prescott, because Prescott is dead! Jack wants nothing to do with it, but the lawyer blackmails* him and tells him he will be sure he's convicted of the crime he's accused of unless he helps him with the swindle!
Once Jack arrives at the Prescott home, he finds that he really likes his supposed step-mother and step-sister (especially the comely step-sister) and he cannot allow himself to swindle them. At the same time, Jack's evil slut of a wife arrives. Earlier in the film, this adulterous woman and her boyfriend tried to murder Jack--and now they, too, want a piece of the pie! But the lawyer isn't about to cut them in on the estate. How can Jack possibly extricate himself from all this and do the right thing? See this film.
Okay...I'll admit that such a story is virtually impossible. Fine. But it's handled so well for a low-budget B that I really didn't care as I watched. And, I'll also admit that the ending worked out too perfectly--but it was immensely satisfying! One of Wallace Ford's best outings and an outstanding film in most every way. If you wish to see it, it's in the public domain and can see at either Amazon or archive.org. Enjoy.
*When I saw this, I thought this was a case of extortion. However, after I did a bit of research, apparently extortion involves a use of threat to steal property from a person--and Jack possessed no property or belongings the lawyer wanted. So, apparently this is blackmail unless I am mistaken.