Did you replace the rear wheel cylinders?
I just put stainless Inlinetube kit into my 64 Valiant and it went well. I went with power boost (the GM version) which has that combo distribution/proportioning block.
I just went from drum to 4 wheel disc on 67. Using the same proportioning valve. Seems to work fine. Same as I installed in 66. That works good as well but only front disc on that. Out of a 67 Newport. But the 67 dart is the original....
