You should be good to go as long as you have the correct u-joint for the yoke in the rear differential .
Use the driveshaft you are presently using in your Dart.
Must be different with a Cuda as I had no problem doing this going from a 7 1/4 to an A-body 8 3/4 from a 71 Demon.
As far as I'm aware, that as long as you didn't change the transmission, the drive shaft would work as long as you had the correct u-joint and yoke.
Going from a 904 to a 727 you definitely need a different shaft.
