Does the lock mechanism work? If not, this could be the broken return spring problem I had on my 67. From what I have read, this is really commom.
If you cannot operate the lock knob up and down and hear/feel a distinct click, this could be the problem.
If it is, you can take a long screwdriver and push the lever on the opposite side of the outside button. Push it towards the outside of the car. You will need the window rolled down for this.
Once this lever is pushed back in place, the lock button should pull up and then the door will open.