Karsten said...
Had to try real hard to think of someone I can recommend - a message in that.
For general diesel engine work, I have heard only good things about John Witchard of Witchard Marine ph: (02) 9979 5480 around Pittwater.
Easy to talk to as well on the phone.
Alternators - for typical low current (30-50A) best pricing probably from Auto Electricians (yellow pages; incl exchange units). For more serious amperage, you need to think about heavy frame alternators that can take the heat - truck size or marine specific; but much higher price.
I must agree, John is readily contactable, happy to provide advice and even recomend others if he cant do the job himself.