What is the best brake master cyl for disc drum

[tracpack440]

1969 charger manual brakes, converted to front discs.   I am having problems with master cyl. The auto zone master  I bought a year ago had worked ok but leaked from the rear seal.
I repl it with the Right stuff detailing master and can not get a good pedal, pedal very spongy. Bought thru summit and already have exchanged it for another one and still having problems. This one is better but still not good.
Masters have been bench bled. installed then gravity bled, then pressure bled. I have the adjustable prop valve open all the way.
Any advise would be helpful
Thanks.

[John_Kunkel]

You haven't mentioned the bore size of the various MC's you tried.

[Just 6T9 CHGR]

When I purchased my SSBC manual disc kit they supplied what I believe to be an A Body master cylinder for manual discs

[b5blue]

  76 Aspen, Raybestos, new not reman. Rockauto about 63.00. I have a 70 Charger with manual drum converted to 11 3/4 Mopar disk.
  Works fine and I use an old school Mopar proportioning valve to the rear.   

[tracpack440]

Bore sizes. The right stuff master is a 15/16 bore.  The AZ bore is 1.031 
Ill look into the others thanks.

[68Charger4me]

The 15/16th bore size will have a longer stroke, took me a little bit to get used to it.  That being said, check for seeping leaks at the discs,  I had a spongy peddle for awhile.  It turned out it was leaking around the banjo bolts and the speed bleeders I was using were leaking.  I also removed the adjustable prop valve too.