This certainly looks a lot like an S&S34 (I own one), which incidentally was designed in 1968. Given your location I suspect you are well aware of this, but there is an S&S34 association down under that might be of help. They can be found at: Sparkman and Stephens 34 Association
Also, Sparkman & Stephens is usually pretty responsive if you have inquiries about old designs. They are located here in NYC and have helped me in the past with some historical questions.
Yep, aware of the S&S 34 association as they are based here in WA. From memory there are three S&S 34's on my jetty. However info on the S&S39 is a bit more scarce, hence this post.
Agree that Sparkman & Stephens are vary helpful. The above plans came from an email response from them
Thanks for all the comments.