how do i fix this?

you can cut that section, patch it, and use a hole saw to make the key cylinder hole. my dad did that for his 64 impala, in the end it does the same thing, hold the key cylinder. imagination and creativity, I don't see why it would be any different for mopar, only flaw is that the cylinder spins a little when you turn the key with force.:-s

I did something similar with a replacement door for my D50 (because someone stole the good door off of the truck). The door I put on was so rotted I ended up welding in new metal (about 90% of the door was gone). I drilled the hole roughly to the size I needed and since I only had one lock cylinder now, I pulled the cylinders from a Chrysler Cirrus and drilled the holes a little bigger (because the Cirrus cylinders were bigger than the D50 cylinders) then used a file to cut the four notches in the holes for the cylinders to set into.