Early A Disc Brake Help Needed!!

First off I will tell you what I have, it's a 1966 Valiant with a manual disc brake swap from a 1973 Duster. All new or rebuilt parts, including all the brake lines. I have 11 inch cop car drum brakes on the rear, also running a Direct Connection proportining valve. I changed the master cylinder over to the newer 2-post style master cylinder with the adapter plate. I have not driven the car yet.

I went to bleed the brakes tonite and I don't have a hard pedal, it goes to the floor. I only get a pedal when I pump the brakes up, but after a few seconds the pedal goes back to the floor. I believe I have all the air bled out, no bubbles left. I did have a couple of leaks but got them fixed. I reused the stock brake rod that came in the car. I do have a Mopar Performance adjustable one but it looked like it was an inch or 2 too long so I went with the original.

Could it be that the stock brake rod is not pushing the piston inside the master cylinder in far enough? Anyone else who has done this could give me some insight? I am stumped and gave up for the nite. Any help would be great, I would like to get this car on the road soon before I have to store it for the winter!! Thanks, Keith.