Hi Grant, welcome. Your boat looks a credit to you inside.
I have a mate with a 4cylinder Volvo, really a Perkins, seems Volvo did the marinising, including the raw water pump which was leaking water into the block. I`ve had a Perkins engine, they are good, and you can get parts, via Brisbane I think.
Are you on Lake Macquarie, or Brisbane water with Hawkesbury access?
2005 Integrity 386 "Sojourn"