WTIA offers seminars comparing the 2 standards. I can't help much, but have made some initial enquiries to Australia about forming an international review group of ASME B31.3. ASME B31.3 is receptive so we're considering how tyo best execute ther workings of such group.
Shane (one of our Kiwi friends in here) could probably explain it better than anyone as he's spent years working in Australia and is also very familiar with B31.3.