GM A-body brake problem

Did the search; read alot. The short of it is my power brakes feel like manual brakes.
1964 Olds Cutlass had power drum/drum. Bought the front disc conversion from OPGI. CPP booster, master, combo prop/pressure valve, braided front lines, etc. Now it takes a lot of pressure to stop.
I have 20" of vacuum at idle.
Pulling 20" of vacuum on the booster made no difference with the brakes.
Booster will hold 20" all day long and won't leak down when applying vacuum through the hose to the check valve/booster
Brake pedal doesn't drop when I start the engine
Brake pedal doesn't drop after 30 seconds when engine is stopped.
After the engine is stopped and I press the brake pedal, the first stroke is soft and then gets progressively harder.

Forgot to mention, the kit comes with a 9" booster. I don't know what bore the MC is.
No light comes on when I check the prop valve with a test light.
Check valve on the booster only allows air out.
The pushrod is connected to the bottom hole in the brake pedal.
I adjusted the rear brakes out until slight drag was felt, then backed it off about a half turn (with the e-brake off).

I bench bled the master and have bled the brakes at least 3 times. No spongy pedal so I don't think there is any air in the lines. The pedal is firm, but takes alot of effort to stop. After the initial installation, and lack of brakes, I replaced the rear wheel cylinder, drums, shoes, and all 3 rubber lines. I also got plenty of fluid from all four wheels while bleeding. No change in the brakes.

I've read other posts where folks have had the same problem but haven't seen a solution posted.
Do I need to remove the check valve from the booster to check the booster?
I am out of ideas and open to suggestions.

I put the car on jackstands and ran the engine. Rear brakes are weak.

Could it be, that the new master is not compatible with the rear wheel cylinders? The OEM rear wheel cylinders are 15/16", which was for a drum/drum car even with power brakes. A 1970 Cutlass came with 7/8" rear wheel cylinder bores along with front disc. If I go to the smaller bore, will it increase the effectiveness of the rear brakes?

The use of an 1-1/8" master will increase volume of the fluid with less pressure. The use of a 1" will have more pressure with less volume.
If the rear wheel cylinders are too large it will take more pedal pressure to stop.
You are more then welcome to call us at 800-522-5004 and speak to our tech department as well.

When pressing the brake pedal, should fluid jump out of the back part of the reservoir like it does in the front?

After talking with Van on the tech line, I pulled the booster and brought it in to CPP. It was bad. CPP replaced it under warranty. Brakes work great now.

thnx CPP.