My 'Cuda wants to lock up and slide way too easy....

If the rears are locking first then something is not right. Factory Disc cars of this vintage had a Separate hold off valve down on the frame rail about 16” from the safety/distribution valve. If all is well it should keep the rear from applying hard and let the front discs do the load First! When we went to Carlisle 2019 I had the left rear wheel cylinder pop on the trip while in the trailer. The distribution valve did what it supposed to and tripped the light and isolated the rear brake circuit. Two new rear cylinders are ordered and only 5 years old.