Sorry, not correct. The residual valves don't hold anywhere near that much pressure, only a few pounds. In fact I just poked nails through both my valves to disable them, but prior to that I had run the car after the disc conversion for a couple of days with the valves in place
To troubleshoot this, you already know it's a brake line pressure problem, so just continue up the line. Get them locked up, then bleed at the distro/ prop block. This will now show if the hoses are what is blocking. Lock them up and bleed up at the master. If this releases them, most likely the pushrod/ linkage is not letting the pistons return.
