So, I just purchased a 1967 mustang(6 cylinder). The front brakes have disc brakes and the rear brakes are drums. The brakes are working just fine up until recently one of the calipers got stuck and started grinding the rotors. i took it to Napa auto parts and they help me depress the caliper, and I reinstalled it, and now my brakes are spongy and when I hit the break pedal it bubbles and spits up minor fluid out of the master cylinder. I was told that I need to upgrade master cylinders and...

Can someone help me with my brake setup