Proportioning valve?

Many years ago, our fist 67 fish, was a slant 6 car. Small drums all around.
Front disc brakes from a 73 Duster went under it first. Later a large bolt pattern 7.25 ( today I cant remember where I got that rear end as if it matters LOL ) for LBP on all 4 corners. Never did upgrade the OEM drum brake master or install a proportion valve.
It would lock and slide all 4 in a panic stop but it did stop.