Hi DT, I have had some fun over summer after a long list of repairs, culminating in a 2.5 hr race up the Barwon. It gets a good handicap because its so old and outlasted some of the more modern cats who broke masts etc. It needed the main pulley replaced, the rudder link bar, the main sheet, all the old rivets to mast & boom, hulls cleaned and filled on the bottom edges, mat relaced, jib has new pulleys to give it a better shape, rust stains removed from sails, top decks polished, etc etc.
Hi DT, Your post struck a chord since I am at Barwon Heads and used to sail a Windrush 12 there as a kid (actually called a Surfcat). It was the precurser of the Mk 1 Windrush from the 1970's I believe. My cousin recently gave it to me after faithfully storing it intact for some 30 years. I'm restoring it now and will have some fun re-launching this summer. It looks very like yours even down to the orange stripes but they had quite a different way of fixing the mat frame (4 SS bolts). The stays were different too and the rudders old-school, fixed ply. A few of the fittings need replacing but its in quite a good state for a 45 yo craft.