Yeah, it's funny how things go around mate, I knocked back a 450 "Silver Shotgun" in 1977 for $450 at Stanco in Melbourne, buying a Yamaha TX500 instead. Oh well. Gowanloch's were in Lidcombe when I was posted there in 80/81 when I was restoring my K1. I wandered in one day and asked them if they did any work on Honda's, and Mr Gowanloch, fresh out of jail (knocking off parts and selling them out the back door when employed by Frasers) told me in no uncertain terms that no, they didn't fix Jap bikes. I was a bit surprised, as they didn't seem to have much work.
If you can afford it, replace as much of the internals as you can, your Darmah is the same vintage as my SS, and the build quality back then was terrible, hopefully the replacement parts are much better now, I presume they're all aftermarket? I couldn't see Ducati having much in the way of NOS parts 40(+) years, and many owners (of the company) later? Selling the 450 should easily cover a complete rebuild, and a holiday, a couple of house payments, and lots of beer.