I just saw a TAS of the Japanese version and the ending looked to be exactly the same as the USA version.
Like I previously said, the script in the English version is completely different. They ditched the original script and rewrote the story from scratch, while leaving the game mostly the same. In the Famicom version, there is no mention of Marion at all and the final boss is supposed to be a revived Cleopatra.
Does each character have an ending and it adds up to a full ending or what?
Pretty much. In the Japanese version, you will only see the endings for the characters you beat the game with. If you defeated the final boss with Ranzou as the only character alive, then only Ranzou's ending will be shown. You need to beat the game with all four characters to see all their endings at once.
This affect the game a bit, because if you're playing the 1-Player mode, you will never get to see Jimmy's ending. You need to play the game with another player or do the trick in 2-Player B Mode that allows you to control both Lee brothers as single player.