I had to refit the shaft 3 times and ask an expert friend to notice this difference, you simply can't see it below the car.
It was a nightmare to find out!!!!!!!!!!!!
If I remember well it is 10mm difference, because the M3 gearbox sits lower, it is a V8... you can reuse the one of the 335i it fits the M3 mid shaft.
My 677mm are from the middle of the hole in the bearing (where it bolts to the car) to the flange surface where it meets the guybo at the gearbox