Thanks Joseph, but it's definitely a 19 foot (5.8m) boat.
Mattyboy, just wanted to say thanks again for all your assistance. I went out to have a look at the boat today and can confirm the hull is splashed from a Donzi 19 St Tropez, but it's definitely not a Donzi.
Some additional research revealed the following which might be useful to know in case a question similar to this comes up in future.
Back in the late 60's a company by the name of Admiral Marine brought the 16 and 19 molds to Australia. When Admiral Marine went bust, CO Jensen bought the molds and began to produce boats under the name of Donzcraft.
Not quite sure which, but it was either Admiral Marine or CO Jensen who designed the deck seen in the above pictures.
Unfortunately this boat is not in great shape and will require a substantial amount of work to bring it back to it's former glory. Negotiations continue
Thanks again Mattyboy