1969 Swinger 340....
1. I did not know that factory A bodies with Kelsey Hayes systems had a main Porportioning valve and then a secondary proportioning valve 8 inches further back ???
They didn't.
See the Master Technician's Conference booklets for details.
start with -
1967 Disk Brakes vol 67-04
1970 Brake Hydraulics vol 70-09
1972 Disk Brake Roundup vol 72-05 http://www.imperialclub.org/Repair/Lit/Master/index.htm
1967 is important because it is the first year of the tandem master cylinders.
1970 is the begining of the change over to combining the valves