I think your brake master is ok the fact that when you have it on the bench and you push and hold for a few min it gets hard and stops tells us that its not leaking around the piston and back to the non pressure side. you can always test it with the peddle and the ports plugged like bench test you did.
The fact that it does not pump up tells us that you either have a lot of air some where or like Joe H said way to much slack in the brake shoes. I agree with his assessment put them hard against the drums then back them off a little. even if its not turning and even if you don't drive it its a good test to see if your pedal will get hard. if it does you know it was brake shoe spacing and can adjust accordingly.
99% of the time you will never have a too small of a brake master if your wheel cylinders are close to the master bore. But i have seen where someone put a lot bigger brakes on a car with a lot bigger wheel cylinder without adjusting the very small bore and stroke length master they had. And it would stop but took a whole lot more pedal travel. Fluid volume is fluid volume if you push out and the wheel cylinder takes a ounce of fluid then a ounce has to be available put push in. Pressure does change with bore size. Match this with stroke length and you have fluid volume. And brake fluid does not compress like air does hence why they use brake fluid.
But I am guessing air. if its not the huck brake spacing.
bleed lines and cap them on end of lines it should get hard immediately. Then hook them up to the wheel one cylinder at a time (bleed the cylinder ) and see what happens.
And your plumbing is correct on master and ports based on your post above.
