Adjustment is the key to these old brakes. Assuming you have good shoes, the system has been bled (no air in the lines), and the master and wheel cylinders are in good shape then a good adjustment will make remarkable improvement in the stopping ability of the stock brakes.
This is the way I do it: run each wheel adjustment out until the wheel won't turn at all, this will center the shoes in the drum, then back the adjustment off until you hear a slight scraping noise but the wheel still turns freely. When you're done at all 4 corners, your pedal should only depress a couple of inches and be nice and solid.
