Soft Brakes

[Murfdawg]

I bought a 64 short bed step side at an auction. It was pretty thoroughly rebuilt by the PO. It has the CPP disk brake conversion with booster and stainless steel lines. Disk brakes in front and drums in rear with a proportioning valve.
It stops fine but has a soft pedal. So I thought bleeding the brakes was in order.
I am not a brake expert but have bled brakes numerous times over the years.
But this time I am puzzled and stumped.
I started with an assistant applying pressure while I cracked the bleeder screw. I GOT NO FLOW! This was with the left rear wheel. Since the brake lines are obviously near new I could not believe it was plugged and so tried all the other wheels. Same result, NO FLOW! I then tried a brake bleeder vacuum. NO FLOW!
I not only cracked the bleeder screw but turned it more than a full turn. NO FLOW! Each wheel cylinder is working just fine and the brakes work, but the pedal is soft.
Help please! Anybody have an idea what is going on? What am I doing wrong?