You should check with a Kubota dealer, however, from my experience, the answer is almost always NO, a deck from one model tractor will not fit a different model tractor. A mower deck from a series 50,60, 70, or 80 is not interchangeable, but all decks within the particular series are usually interchangeable. What tractor number does the RCK54-15BX originally fit? The "15" would indicate to me that the deck originally was mounted on a BX1500, which is a 2-cylinder tractor built back in the early 2000s.