Am I correct to assume that the BMW sourced components are ISO whilst the Mazda gearboxes / engines are JIS.
I don't believe it makes any difference for spanners, the standards mentioned appear to apply only to max/minimum of hole sizes, the thread forms (metric 60 degrees), sizes, and pitches are the same across the standards and in nearly all cases (especially in the common sizes) the ISO and JIS dimensional limits are the same as well.
So in terms of spanner sizes, they will always be the same, and although it's theoretically possible that you could find that an ISO bolt wouldn't fit a JIS nut of the same size, the chances are so remote they aren't worth worrying about.
