No offence taken..
actually that was just one broken shaft that we physically had sent to us... We have had quite a few people ring up with problems when going from a 2 piece to a single. There was 3 in a 2 weeks period at one stage.
Yes AU's have IRS and a single piece, and no issues really... In saying that we have fitted quite a few 2 piece shafts in the sedans and utes. When Mal fitted a T56 in his AU XR8 years ago he had issues with a vibration, tired everything to keep the single piece... Fitted a 2 piece and vibration gone.
The 2 piece shaft in my work ute (VE-SSV) was made using XR6T parts, has never been balanced, and at 224km/h it has no vibes.
Also, I'm pretty sure the V8SC's use 2 piece shafts, as the guy we get to balance out tailshaft a builds the shafts for Triple 8.
You can use an F series centre bearing, however I am pretty sure you will need to change from a rubber coupling at the front to a uni joint.