**71 Dart wont start after CAM, Timing Chain and HEAD Cylinder install** HELP

Like said, if you didn't pull the D out before the cam removal, then pulling the cam would have rotated the rotor to a new position. Then installing the replacement cam would not necessarily have rotated the rotor back to the proper orientation. I have never tried this and didn't even know it could be done.
Any way you just need to reset your timing, as others have said.