D&D Disc Brake Question

Guys I installed the d&d disc brake conversion to my 64 van and just cannot get the stopping power I need. I have disc front and drum rear and all the brake parts are new. I questioned the po of d&d quite a while back to see if I needed the proportioning valves installed and he said since I was using the carquest master cylinder #20-2203 they are built in the cylinder. I have bleed the brakes over and over so I don't think it has air in the lines. When bleeding the rear brakes the pedal goes to the floor but when bleeding the fronts the pedal only goes half way to the floor. Anyone have any idea what my problem may be????? Thanks

Couple thoughts: Drum brakes require a 10 lb. residual pressure valve (RPV10) to counteract the spring tension in the drum system which tends to pull the shoes away from the drums. Do you have a RPV10 on the line running to your rear drums? If not, you might end up with mushy brakes.

Also, where is your master cylinder in relation to your calipers, above or below? If below, fluid might be draining back into the master, which would hurt performance. One last thing, did you bleed the master cylinder itself, or just the four corners?

Here's a discussion on Brake System Configurations