There is a Sierra IRS on a Locost chassis design called Rorty Locost:
http://www.locost7.info/files/suspen...RSAssembly.pdf
It looks quite similar to the Haynes Roadster rear suspension, I guess you'd be able to adapt some of the Haynes components, rear uprights and maybe wishbones. Keep in mind that Locost is 2" narrower than Haynes, you might have to shorten the Sierra driveshafts.