I fited one to my track 1600 - went from slight predictable understeer to more neutral handling. Downside was that when the rear did let go, it did so very quickly and was harder to catch.
I don't know if you'll find anything to fit from other models, but there are a few aftermarket ones around. I'd go for an "over the top" type of fitting rather than an "under the trailing arms" style one as they hang pretty low and are succeptible to being ripped off on tree roots when reversin g down your driveway (that's my experience anyway
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EDIT: You can actually see it hanging low on the left hand side in my avatar