That's actually a more impressive hack than just swapping Mario and Pauline (which itself requires all new animation for Pauline). The NES version of the game doesn't have the conveyer belt stage, or the end-of-level animation of DK climbing to the next stage, but this hack has both.
Bravo on all levels.
Very belated edit to note that while the NES version didn't have the conveyer belt or the end-of-screen animation, the "25th anniversary" version released for the Wii store did. Still, though, Bravo.