My 64 didn't have locks so I went straight to electronic. I installed a set from Electric-Life. Very easy to do; install the module under the dash, bring unswitched power to it, run the wires into the doors and install the actuators near the latch mechanisms.
Now when I lock or unlock one of the doors, the other does the same. The also have a remote version, but I stuck with using the key. There is lots of room to mount the actuators, the only thing to watch is to keep the rods as short as possible so they don't flex. I think it was just over $100 for the complete kit. I has to add some extra wire inside the doors, but no problems to do.
Hope this helps
Terry
64HT