Parking brake stuck
These old Fords were notorious for the cables rusting in the housings at the rear. So you need to find out what went bad, so start there and work your way forward.
Look at the parking brake pedal, it has like a ratchet mechanism to lock it in place. See if that's working ok, if it is, look at the brake shoes in the rear wheels to see if the cable is releasing. Parking brake is strictly mechanical, does not use the hydraulic system like the regular brakes
Go under the car and find the cable and the spray the hell out of it with WD40...
The linings for the parking brake shoes probably disintegrated from age. I've seen this before. What happens is a piece of the friction shoe breaks off and gets lodged inside the drum portion of the of the rear brake rotor. You'll probably have to remove the back brakes and rotor and completely replace all the emergency brake components, including springs.
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