I can't see the pictures but the size of the slots are not your problem , there are thousands of big block mopars out there with the same head gaskets.
I have a friend that had a similar issue that nothing he did would fix, his engine was also .060 over ....
I have to agree with John. I think at least part of the over heating issue you have is your .060 over bore. That much bore usually makes a 440 engine run on the warm side. Boring a 440 motor.060 over is great for a race engine that only gets run for a few minutes at a time, but not a street driven car. Is this a numbers matching motor to your car?
