I went to my local wrecker and sorted through the shafts from all the various different IRS equipped Commodores till I found 2 that were close to the length I needed. They all use the same 6 bolt pattern for the flanges.
Since I used a mix of Ford and Holden stuff I ended up making my own drive flanges for the suspension uprights. This let me me mess around with the lengths in the flange dimensions.
You can see how I made the new drive flanges in these pics.
Cheers