[enollava]

If I got this correct, there were two 6 speed versions in japan. The GTO MR wich was a 6 speed with an "MR" gearing in front. This one used a 5 speed rear diff. Then there was the regular GTO wich was also a 6 speed and used the same 6 speed rear diff we have. If you have an MR transmission, you need to use a 5 speed rear diff cause the MR diff changes the front final drive ratio as compared to the US market 6 speed, and it matches with the US market 5 speed rear diff. If you don't use a 5 speed rear diff, you will cause serrious problems with your transmission cause the rotations per mile on the rear wheels will be different than the rotations per mile on the front. I think this would cause your VCU to go bad and might cause other issues too. Anyway, I'm sure some people with more info on this will chime in and add more to what I said.