Yeah, I agree BDI. The Cr's let you slip extensions into the swing arm because it is hollow at the end. The strongest way to make them for Kaws is a complete swing arm made from chromoly. I think you all would be shocked how inexpensive a custom set would be. It may be a little more than welding some off-set aluminum blocks together, but you will only have to buy chromoly swingarm once.
Js, I doubt very seriously that an Ice dragger is putting more stress on a swingarm than a 4 cylinder nitro-methane burning hillclimber injected with nitrous on a pro hill with several jumps. I can't imagine a flat surface being more stressful than that.
The thing about extensions that you need to keep in mind, that I think is being overlooked here is, a good set of stretchers are very adjustable. Depending on conditions, gearing and tread pattern, you will want to be able to make length adjustments for more or less hook-up. Usually guys have a slick set-up, dry set-up, jump set-up or drag race set-up. These may require different sprockets, length of swingarm, rear wheel and of course that all means length of chain. A good set of stretchers makes these changes quick and easy and you won't be stuck with just one set-up.
