Wow nice schematics
i love the paint job. As for the lenght, i found out that we got a lot of adjustability.
I wasnt supposed to use it but i ended up puting a N55 prop shaft, so it is 15mm longer than my original N54 shaft and was cut to 1339mm instead of 1325mm but still working fine.
It is most def not that big of a job as everybody thinks, more people should try it. Hardest part was getting the old axle shafts out...
No balance issue, the shaft was balanced by GKN and i used a black bolt on the blue mark of the input flange of the diff. So far so good and no vibrations.
As for the cost, if you're patient, it can be pretty cheap.
For me it was way cheaper than any other options.
Diff: 650€
Axles: 200€
E60 M5 prop shaft: 190€
N55 prop shaft (was intended for backup but i ended up using it): 200€
Cutting, welding and balancing: 160€
Bolts, reinforcing plates and stuff: ~50€
I paid way too much for the M5 shaft... But i would do it all over again.
Next step is to ditch the GKN viscolok and go for an upgraded e39 ZF diff.