Yesterday I took another look at those Korts. I had decided that they were not as I wanted (nor even as described by the manufacturer), and I had prepared myself to either buying or making another pair. So I had nothing to lose if I tried to modify them but stuffed them up.
I decided that the major issue was the nozzle length (50% too long) and wall thickness of the nozzle (50% too thick). I couldn't easily do anything about the thickness, so I decided to cut off the excess length and see what it looked like. The thicker (inlet) end seemed the logical choice here, so I cut 13 mm (1/2 inch) off from the thick end.
If anyone else has any similar ideas, be prepared. The dust from cutting, filing, sanding, or drilling this stuff (HardyCast) is not good. Wear PPE - dust mask (a good one), eye protection(goggles rather than glasses), surgical gloves, etc. Disposable overalls if you have them, or be prepared to throw your clothes into the laundry immediately after you've finished cutting - and jump into the shower yourself. Definitely use a dust extractor if you have one; and use a wet cutting system if you can.
I don't know how the manufacturer can ship this stuff without an accompanying MSDS.
Anyway, after cutting the nozzles to a more acceptable length I was left with a "square" edge to the inlet - so I sanded it until the inlet was fully rounded. The final result, although still too thick at the inlet, looked a lot better than the original, so I decided to keep these, and use them on my project - at least now they will fit under my hull. But I probably won't buy any more from this supplier.
The material itself I found to be easy to cut and sand using a Dremel diamond cutting wheel and sanding drum. It didn't respond well to a small file, but did sand well with wet-and-dry paper for finishing.