Given that your propshaft only takes (as standard) A maximum of 50 % of the available power & has the slip from the VC unit at the rear end,
why would you want to bother with this conversion?
I remember back in the day when Ralle Mike (Audi doody) was running his Rallye with a chipped 300 bhp & he was buing 02C gearboxes & (Rallye cast iron transfer boxes) from me on a regular basis but did not have any problems with his propshaft running the std 90mm joints.
Same with Nutter 4×4 who had transfer box problems with Rallye (cast iron) transfer boxes wich kept blowing the aluminium right hand fwd drive end plate off but again no propshaft problems
so what power are you running to need this mod? please tell