There's a great locksmith in West Sac here that I had re-key the door locks on my 68 years ago. He's an older gentleman who loves old Mopars. When I brought in the door locks, he knew right away they were for and old Mopar and asked that I drove the Dart when I picked them up. Really nice guy. He works out of this shed in front of the Raley's on West Capitol and Westacre.
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After looking into it though, it's actually not that hard at all, especially if you have an abundance of lock pins from old lock cylinders on hand. I ended up re-keying the door locks on my '66 not too long ago and just did the ignition lock cylinder last weekend to match. The ignition lock cylinder is a tad more intricate because the plate that holds the pins and springs in is swedged into the cylinder casting so the springs and follower pins have to go in from the cylinder side. Still very doable though. I can walk you through it if you want to give it a go!