Disc Brake conversion power master cylinder question

I'm having the same issue, sort of... i have 4 wheel drum, booster, and dual res m/c. New wheel cylinders, rubber lines, shoes, drums, and the pedal pumps pretty stiff but the brakes just don't stop the car. I put it on my lift, start it up and put it in gear and the rear spins away, apply brakes and it will slow the wheels but with full pressure on the pedal the wheels still move. Pulling my hair out over here! Any thoughts will be helpful !

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