I'm going through this exact same thing on my 65 Valiant. However, on mine, the MC piston came out with pushrod. So now I have to get the piston off the rod. Will probably grind/cut it off.
I did the same once. A few shims and my ball joint splitter separated it. So thats what I use to begin with now. Never had one so tough that I had to hammer the splitter. Just used it as pry bar between shims and vise.
