I think the first thing to do would be to try and get the rear sections from a CLS55 on ebay or something, then get an exhaust fitter to put them on and fabricate everything else to fit
try torque flow in small heath birmingham, they should be able to do it or point you in the right direction.
Or Acid ( Brabus K8 ) at MSL on armoury road, small heath, he can get nearly everything and at a reasonable price