1960 Chevy Bel Air brake will not release

We are working on a 1956 chevy, with new brakes, after driving a few miles, the brakes lockes up on it. We waited aa few minutes, 10-25 minutes they released themselves. We took the brake drums off an stept on the brakes, they expanded put did not released. So we took a mallet an taped on the brakes, to get them to released the preasure an close, but they did not.
A friend says that the problem is in the master cyclinder because he thinks one of the holes in pluged an not released the presure.
What do you think?
Rick
rge47@frontiernet. Net