HOW DIFFICULT IS IT TO REPLACE MY 67 BARRACUDA DOOR HANDLES

Did you read thru link I posted? Take pics prior to disconnecting linkages. Maybe spray clips with silicone to help keep them from breaking.
Are you sure you linked the correct story?
Most all that was about the doors and hinges.
I did find a good video on YouTube though.
I'll probably tackle the non-driver door handle first.