Did you just do the wheel cylinders, or the master also? If you did the master, make sure the rod on the brake pedal that goes into the master cylinder is adjusted properly. It needs to allow the master cylinder piston to fully retract to pump fluid properly to get rid of air. I can't remember the exact Bently measurement of free play, but it sticks in my mind it's less than 1/16th of an inch. At the wheels you can check a couple things. The later cars had a slight angle on the base of the brake shoe where it sits in the adjuster. The adjuster also has this angle for the brake shoe to sit in. If you look at the adjuster where the slot for the shoe is cut, there will be an area where the slot is cut real deep in the adjuster, and on the opposite side the slot will not be cut very deep. The area with the deep cut slot goes upward. If this is incorrect, the brake shoe won't properly seat against the drum, and cause a very similar issue like you're describing. Also run the adjuster all the way in, and adjust each side equally when adjusting the shoes. Adjust them until they completely lock up the drum, then back them off till they drag slightly. If you haven't replaced the brake hoses, I would do them also. A collapsing brake hose can require more pedal pressure to get fluid through it. Also a hose delaminating can swell up like a water balloon when fluid finds its way into different layers of the hose causing the pedal to sink.