I'm not sure about a Cuda, but on a Challenger there are 4 screws on the front of the heater/blower box under the passenger side dash. Just remove the 4 screws and about 6 clips that hold the 2 halves together. Take the front half off and the heater core will slide right out after detaching the heater hoses.
Just be careful removing the metal clips, the fiberglass box can be real brittle. I used a small screwdriver to pry them off.