Yeah, very odd way of going about things. A z4m diff carrier for example could be had for £100 or so to fit the e9x m3 diff (which is the same as the z4m), but no, let's butcher a standard z4 diff carrier :? Weird. Then try fit an e9x front subframe??
Love the idea but the execution seems ill thought out.
This guy had better ideas, never finished though afaik.
https://www.zpost.com/forums/showthread.php?t=1364034