I don't think each weapon has to be exact, but if there's something that works just as fine without changing drastically, that should be used.
To avoid using another Fire recovery move, I think Wing Spiral would be fine, just have MMX go up even higher when he does the attack. There's also the Mach Dash from the Blade Armor or the Falcon Dash. There's also the MMX8 version of the Shoryuken, which looks a bit more like Ryu's, but I'd probably give him the MMX2 version anyway.
Storm Tornado could be an Up-Smash, and if not that, Shining Ray from MMX8.