rear brake problem

[Dans66SS]

Just replaced the single bowl master cylinder on my 66 Chevelle with a double bowl and power booster for drum/drum brakes.Also replaced the distribution block at the frame.( All this came as a 'kit'). having trouble getting brake pressure to rear brakes. Have fluid at both cylinders but when pedal is pushed,no brakes. Front brakes are locking up but pedal almost goes to the floor. Any suggestions please. Thanks Dan...