Goto a junkyard, buy a stock exhaust for an E350 PSD, take it to your local muffler shop, tell them you would like a quote for a 4" or 5" exhaust system fitting the dimentions of the stocker you just got. You could also ask the companies you listed to fab you up one from a stocker exhaust. (You would probably have to pay them for the stocker and give a pretty substantial down payment since it's going to be a one-off.)