Classic/Antique Car Repair: 50 plymouth brakes, rear brakes, rear drums

Question
I'm cleaning up another mechanics mess right now, something I'm not fond of. The symptoms are soft pedal and pedal won't return by itself. I have bled all the way around twice and inspected the front shoes. I'm trying to refrain from pulling the rear drums just yet. The front brakes did look good though and the return springs felt like they had plenty of pull. All of the wheel cylinders have been replaced along with the master cylinder. Any tips would make my life a little easier because this car does not belong here we are not a classic car shop but it was here before I showed up, so it's my job to make it right.

Answer
At this point you have no choice but to address the rear brakes. If you feel they were replaced by previous mechanic, you could try just adjusting them, but if not that may do more harm.

Beleive you are over extending the master cylinders ability to recover (i.e. back brakes are too loose).

Does putting on the (working) emergency brake help the pedal? Dead give away problem is rear brakes.