Nice clear pic, but it is difficult to tell the size of the crownwheel bolts (however they do look smaller than 17mm). I uploaded an edited version of your photo and circled the bolts in question - if you still have the diff out of the car, then if you just fit a socket onto one of those bolts you can tell what size it is.
I am aware of the crownwheel bolt size differences, but I have contacts whom do this sort of thing for a living & I'll be talking to them in depth when they return from holidays on Monday... so I do have more than just a passing interest in this diff.
Also do you have any idea on shipping costs from Perth to Sydney?