Tight Handbrake

OK got the front cable removed. Like the OP the adjuster nuts didn't free up, and just twisted the threaaded rod in half. Cut the other lock nut off and was able to remobe the cable/housing from the car.
This cable for the 64-66 is unbotanium, but the good news is the housing/sheath is the same length (41") as the housing for the 67 & up Valiant.
Raybestos part # BCA 92319 is $21.79 at Rock Auto.
Cable Diameter (IN) 0.125
Cable Length, Overall (IN) 92.500
Housing Length, Overall (IN) 41.000
Wire Fitting Size, End 2 (IN) 0.313
Wire Fitting Type, End 1 Clevis
I'll just run the wire through the fitting in the '64 intermediate cable, use a cable clamp or 2 to secure it and cut off the excess, leaving a few inches for adjustment.
If this was an auto trans car I wouldn't be concerned, but since it is a stick, I use the parking brake.