I had an idea in my head that the driveshafts for an auto box are different lengths than for a manual. But could I find reference to lengths or CV joint size? Haynes is next to useless on this one.
7Zap.com lists several part numbers, but just the right side for an auto. Not both.

Anyway, had a chat with Mark over at Classic VW, very helpful chap. He asked me what diameter the CV joint was? Err, hang on, will have to call back when I've measured it. Several days later after sourcing an 8mm splined driver and extension plus a ball splitter for the tie rod end, I called him back.
It's a 90mm joint and 560mm total length for the guest side. 20mm more than the standard manual gearbox.
As a side note, I'm sure there should be some grease packed in there, and a gasket?
I have tried in vein to find these anywhere else. Yes, I could just change the split boot. But I have clean(ish) OCD. Who knows what state the joints are in too. Anyway, Mark says he'll order a set for me.
As you can see, seen better days... not to mention that original wishbone, messing with my OCD big time!!