Whats wrong with this brake combo

[waynieZ]

My friend has an early 90's S10 Blazer its got a 355 ,turbo 350 with a 10 bolt in it. The brakes are disc / Drum. Stock I think. He had a Corvette 1" master on it with no booster (not enough vacuum). The brakes are hard as a rock with hardly no pedal travel. He said its like stopping a Mac truck. It has no residual or prop valve in the system. He changed to the factory S10 brake master and still the same. Not sure if it was for manual or power set up. Need help fixing. I think the brake set up came from Master brake systems. They told him to use that Corvette master. Does it make a difference which part of the master you connect to, front bowl for the rear and rear for the front?
Thanks