Here's the way I'd approach it...
Lock the brakes up again and then crack open a rear wheel cylinder bleeder to release the pressure (check both rear wheels after opening only one bleeder)...did that release the shoes? If that releases the brakes, do it again and this time crack open the bleeder on the Hydrovac...if they stay locked up then it's the rubber hose acting like a check valve.
If all of the above does nothing them than you have bad wheel cylinders, broken return springs or trash in the cylinder not allowing the piston to retract.
Hope this helps,
Mike B
