Cheers mate, will get in contact with him.
Yeah that's exactly what has happened, previous owner was obviously a bit of a muppet.

Gidday guys, Is there anyone in the South Island (preferably close to Blenheim) who may be able to point me in the direction of an engineering firm or race gear maker etc who can weld and strengthen my dog clutch in my rear diff? At current the teeth on my dog gear/clutch have worn down over time so ...

Nice Rig mate, good to see another tough looking Surf around. Here's a pic of mine, taken a while but finally got there.
Looking forward to seeing some more progress on yours.