Drum to power disc?

Power assist is a different question than disc brakes. A-body power boosters sit on stand-off brackets with a lever system for the pedal and rod. Look for photos. If Volares have the same setup, it might fit. Just measure the firewall bolt pattern and consider hood clearance.

In changing from front drums to front disks, you will need a proportioning valve in series with your rear drums. Factory ones can be expensive. Perhaps you can use the one on the Volare. I put an adjustable one on my Dart, $28 new on ebay and many posts here.