SO, I went ahead and installed the 99 C3500 1 Ton Master Cylinder. I bought it from O'Reily's. Part Number 10-2754. To make this work, I had to buy two Master Cylinder adapter parts so that the front brake line would screw into the front reservoir and the rear brake line in the rear reservoir. The lines will physically fit in the opposite ports, but that's not where they belong. So, I went to Pep Boys... O'Reily's and AutoZone did not have them... everything bolted up easily. I still need to bleed the master cylinder and then the brakes. We had a cold front blow thru that is keeping me indoors.
Part Numbers:
1999 C3500 1 Ton Master Cylinder
O'Reily's Part Number 10-2754
1/2-20 to 9/16-18 9/16-18 to 1/2-20
AGS BLF-21C AGS BLF-26C
Edelmann 258307 Edelmann 258306
Weatherhead 7913 Weatherhead 7912