Hy '37 barn find, To bench bleed a master cylinder loop a short piece of steel brake line from the discharge port of the master back to the reservoir, submerge the end of the line in the reservoir fluid so you can check for bubbles. Now with whatever tool you have that is appropriate push the master cylinder piston in and let it return all the way to its at rest position do this a few times until all the bubbles disappear from the fluid in the master cylinder reservoir. Once that happens your master cylinder is successfully bled. One other thought I had is, did you adjust your brake shoes up before you bled your system? Hope this helps.