After doing some reading about 4x4 truck rear disc conversions I decided to try leaving the stock 75 valve in the Valaint when I went to 4 wheel disc. It stops very nicely without any extra prop valve.

If the brake proportioning is right for drums ....its likely right for correct sized discs. I used Explorer 8.8 rear and discs.

Id try the stock setup before messing with anything extra.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

To swing the thread back, as I'm talking with the previous owner, Delphine (the Dart) always pulled right. Also the master Break cylinder is from a 75. Is it common to change the Break cylinder when doing a disk conversion?

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My Car Domain

I agree with dakight and emsvitil, your problem is probably a caliper or hose. You can convert an all-drum master cylinder by removing the residual pressure valve for the front brakes, but it wouldn't be as good as a purpose-built one, where there is a lower pressure valve for the front. That way the calipers are ready to go, but not dragging.