[jeffahart]

What is your locking symptom, Locks up when you press pedal and pedal is hard. OR, locks up and stays locked. If you are staying locked then I think you have he wrong rod or have misassembled it. Hard pedal is possibly lack of boost, and I'm going there first because it's a new setup you are getting up. How is your hydraulics plumbed. Can you show your setup.

You mentioned something about stock! Were the brakes fine then, you swapped the master replacement now bad. I am under the assumption you did a conversion since this is the 67-72 area. But more likely you bought something not stock I'm thinking.

I noted ABS in your post. Also, are you sure you have a hydroboost? An, HV caught my eye there on your last post! What is your setup. You may have bought a custom rig with some nice components if you got ABS. If that's the case you could tickle the manufacture.