71 demon brake questions.

yes i have bench bled the master cylinder, its for a 1973 plymouth duster with front disc and rear drums, rear brakes are adjusted, and im getting fluid to the front calipers, just not keeping pedal, although i have been pushing the pedal all the way to the floor when bleeding, but if this messes with the combination valve will it automatically recenter itself or will i have to take the brass plug out and do it manually, i dont think its stuck because im getting fluid to all wheels. also i think the rear wheel cylinders are for a 71 duster with 10'' drum brakes. but to see if the combination valve is stuck im i turn the key to the on position and hit the brake pedal to the floor the brake dummy light should come on right?

thanks for the info guys.