Ta Dah! The refurbished 300 driveshaft and another little tick in my/our understanding of these cars.
Both CV joints are GTA/A610/R25. The only difference is in the length of the driveshafts, the 300’s being longer at 830mm.
The solution to my problem (a sheared off nut) was to find a driveshaft with a good hub joint.
Thanks to Clee for the driveshaft from the infamous Clarkson A610.
Thanks also to Driveshafts.co.uk in Willenhall, Staffs for a fast turn round and the mating of the two (swapping over the end splines and refurbing the whole)
Also FYI, the 300’s rear wheel bearings are Ref.PWK0082 (Premier Vehicle Bearing Componants). BMW apparently.....
Inner Diameter 45mm, Outer Diameter 85mm, Width 41mm