My buddy built a two into one setup for his rat rod with 3 spare HC1's. Since they're 50mm turbos, nobody seems to want them, but they worked good with some elbow grease. 60-70psi was no problem, and they didn't even have the same size exhaust housings. Just remember that smaller is better for triples. A stock HX35 can support 450rwhp, so there' no reason to have 900rwhp worth of turbo on a 400rwhp truck. It will actually cost power to spin more turbos.
Anyways, here's the link.....
http://www.dieselpowermag.com/features/ ... bo_system/