Help! Tons of Pedal Travel

[captchuck]

Hi all- I have searched the site for info- and I cannot find any specific answers.

Here is what we have-

1971 F250 2WD
Ford Factory Front Disc/Calipers
Rear Discs from a 1980 Cadillac (Lugnut Conversion)

New Brake Lines
New Brake Hoses
Removed Metering Valve and Brake light switch
New Master
New Booster
Added Wilwood Prop Valve

Pedal travel is insane! I have to move the pedal 6" or more before brakes start to grab. Power bled the system 7 times. No leaks. No air that I can detect. I have checked the distance of the booster rod a few times with a caliper. Looks to be correct. Bench Bled the Master. Not sure what else to do? Perhaps the MC because it was originally a disc/drum unit has some delay in it for the rears?

Any ideas or things to try?

Thanks!!!