the octane difference is, of no concern. i've known TONS, including myself, that have ran jdm ecu's with 91 octane, and had no detonating problems.
i'd like to know if the ecu will operate the engine and whatnot correctly. i dont want to find out there's differences with certain sensors or whatnot that will result in things not working...
AR99NSX, gimme that ecu in your avatar! man, i want a mugen ecu for this project, like my last. sorry, you can't help, cause you're running a jdm ecu on a jdm spec car.