To my knowledge, the only way to equip the Masamune onto Cloud is to edit one of his swords to use the graphics that Masamune uses. I've seen screenshots of this done before, but I cannot recall an actual patch for this existing. For that matter, I also haven't seen a patch that simply lets you play as Sephiroth. There's the patch that completely changes the game, and you can force him into your party using the Jenova game save editor - as a computer controller, game breaking character.
In otherwords, unless someone can prove me wrong, if you're looking for a quick download to grant your wish, it just doesn't exist yet
EDIT - Try changing the subject of your topic to reflect what you're looking for. If someone does in fact have it, it'll increase your chances of them reading this.