i had something similar..changed the rear shoes on my wagon. (gl,1.8 ohv,carb)
brakes all the way to the floor, had to pump numerous times to stop. bleed the brakes front and back same problem.
solution..changed the brake booster and master cylinder. wow let me tell you its better than ever, i never knew how crappy where my brakes..
cost brake booster 150
master 40