1965 Valiant brake woes
Just a thought.
When I converted my 65 dart to dual master and Kelsey Hayes disc's, I replaced all of the lines and a new dual distribution block. Also found that 67 is different from 65 is different than 64 and 63 on the distribution blocks.
Inline tube sells all of them and stainless lines. Their dual conversion for the 65 is also available in pre-bent stainless, won't rust, corrode or give issues. I bought the whole kit, and replaced every line and hose on the car in the process. I only had to bend one line on the install. And straighten the long one as per instructions.
My three pump 10" drums went to a no-pump stock manual disc setup. They had been soft since the 80s. Found the crossover line to the passenger front was almost rusted through as well as the line to the back.
A pic of the correct 65 proportioning block for the conversion and the kit.