Interesting drum brake problem

Had this as well
69 Dart drum on all corners.... The prob turned out to be, the drums were at there machining limit maybe even a little more. New shoes helped but as soon as some wear on the shoes took the tolerances down.. the front breaks lock up.
I see one of the other members also mentioned this. Springs, cylinders etc become over extended as well as the piston in the master, thus the reason we tend to think master issues. Once I installed new drum (ones that meet spec) new shoes need and cheap anyway POOF all groovy again!