Naruto RPG uses standard Shift-JIS text encoding, which is processed and displayed according to a kind of internal character table - like "if SJIS character 0x8140 is encountered, use 8x16 NRPG character 0x00" or something like that. Also, if you just replaced some Japanese characters in the fonts with English ones, dumping and inserting the script will be more difficult I'd imagine, you'd be better off relocating the font(s) and relocating and expanding the character table. I'd help you more, but my own project files for Naruto RPG are on another PC I don't have access to right now... (My translation attempt on the game is halfway abandoned, btw, because of the lack of a translator as well as screen space restrictions and my attempts at a half-width or variable-width font failing)