I looked at the thread about Richard Mann's rear suspension mods and from what I can understand, the interior CV Joint is from an Alfa Alfetta. That is very interesting! I'm writing him about any details he can share about that.
I've posted some pictures of the CV joints I bought from Richard. Unfortunately, the parts were wrapped in duct tape many years ago and taking it off left a fair amount of goo so you'll have to look past that goo and my poor photography. The first two pictures are of the main, outside piece and the third is the interior piece where the axle splines would mate. The splined collar fits over the output shaft of my NG3 and I believe any other Renault tranny a Europa owner would likely have. The offset hole for a roll pint also matches up with the output shaft. So, as I described earlier, one plan might be to cut that collar off that CV joint and weld it onto a "generic" or VW CV joint flange. I believe what SwiftDB4 posted a picture of is something just like that.
Using a VW CV joint flange would, I think, allow you to replace the rest of the drive shaft parts with VW parts - although there might be some massaging necessary. I would experiment with stub axles if I had a junk rear upright I could test fit with. Someone???
It might also be that BMW parts would fit too but there are lots of VW parts to choose from. For example, drive shafts come in one inch increments, stub axles are hardened and all are well made, readily available, and economical. Also, all the splines would immediately match up.
That's at least my initial plan. If someone has some concerns or ideas for alternates, I'd love to hear them!