Check out some of the mid 1970s Chev one ton pickups. There where some of them that had the hydro brake setup. My Grand Dad had a 1976 that had it. It would slide the rear wheels loaded. They where wicked empty.
I have a 1985 Chev 3/4/C30 ton diesel pickup and it has the hydro boost setup too.
Look real close at your setup. On the 1985 truck the master cylinder and the booster where just bolted together. You could replace the master cylinder without the booster. I have replaced it twice and it was under $150 each time. The booster never has given any trouble.