Just realize that's setup to fit an 05 GTO chassis, so you'll be modding a lot of it to get it to fit your car. Not sure the manifolds will work either; they use the stock GTO exhaust manifolds turned around, but they may have clearance issues on the Chevelle.
Nelson Racing makes a set of headers that will fit the LSX and your 70 Chevelle; you could run twin turbos or a large single with them.
Jody
very impressive what kind of power are you looking for.