Near as I can tell, BMW only uses a couple different CV bolt patterns, would be an interesting exploration to a U-Pullit..
If your already going to the so much work to space frame and build double wishbones, heck just use a large case rear diff, add the mount points and pick the parts to use the 7 series brakes axles and diff.. Thinking furthur,, I wouldnt even use a BMW rear, I'd order a Dutchman (
http://www.dutchmanaxles.com) IRS 8.8/9" or use the rear out of an ford SUV several are now IRS, so you can have a good locker and a diff that has many gear options. changing the CV style rear axle lengths is trivial cut it over-tube it weld it done. 1 hour job. The Dutchman rear uses 935 CV joints, so easy to get and theire are knock offs that are good quality and relatively cheap.