The 2002, E21, 4 cylinder E30s, and, by extension, 4 cylinder Z3's received various versions of the 168mm rear. BMW recycled it into the E53 X5. The different versions had different widths across the carrier bearings. The 2002 width went into the front of an E46 (or maybe E34?), while the E21 & E30 width went into the front of the E53.


The front drive axles are very different than rear drive axles. That's another aspect of the project I'll have to tackle.