Chad, congratulations! You found out on your own the same things that I found out 5 years ago, some guys don't bother to put in that much effort. I recommend that everyone starts working on their arrows at least a year ahead.
I found NO valid information about asiatic water buffalo 5 years ago and very little about bowhunting for cape buffalo. I too tried contacting people in Australia and the only info I got was a warning not to hunt with one well known outfitter there, good info by the way. I did get BAD advice from a bowhunting consultant here.
I recommend that guys shoot for the top of the heart, lots of high pressure plumbing there and the heart is the size of a basketball. A little low is still in the heart and good, a little high is still in the lungs. A buffalo is hugh, mos guys think they are closer than they are, but still think about the size of a full sheet of ply wood and you won't be far off. The kill zone? Its tough to answer, I'd say the heart and lungs cover a two foot circle, but you want to put your arrow close to the center. Shot distance, we had several at ten yards this year, but that is really TO CLOSE, in both those cases the buffalo happened to walk towards the stalking hunters. It is very difficult to get closer than 35 or 40 yards, but possible. I depends on the particular buffalo and where he is at. Herd bulls and almost impossible for bow hunters without a LOT of luck, just to many eyes and noses. Rick