Some help/input

So I just recently converted to kelcey hayes sbp disc brakes in front and have 9 inch drums in back. I have prop valve installed and 15/16 aluminum mc. For some reason after the car sits when I'm at work for 12 hours the pedal will go to floor, after driving it and stopping numerous times the pedal does pump and stays firm after. I have already bled the system twice and no air in system. I dont know what is causing this long pedal travel as I have the pushrod measured correctly. I bled the mc as well. I was told that these mc font have residual valves for rear? So could that be a problem or maybe air trapped in multiple locations of the lines that collect when car sits or? I've been trying to diagnose the problem for 2 weeks now. Do I need to get certain rear wheel cylinders that have a residual valve in them or what? Any input or opinion will be appreciated I am pretty stumped by this.