Converted a 69 to power front Disc brakes, 10 bolt to 12 bolt. All components are new. Bench bleed the MC, bled all 4 wheels. Pedal feels good until the engine is running, pedal goes to the floor. Short rod with a shallow MC, good vac to the booster, lines off the MC, distribution block and pressure valve to the front brakes all leak fluid when opened to check for blockage. I am stumped as is my mechanic. Any ideas what to do next?