You could always make your own manifolds. Thats what Ive been doing for my 240D. There is one place in Aus that I know of that has, or used to have when I last visited, 2 factory Turbo OM617's. One was installed in a G-Wagen. PM me if you after the contact details, they are located in Salt Ash, NSW

One other thing, I'm not sure if your cars have a heat shield around the rubber flexijoint on the steering box input shaft. At any rate I dont think your converted 280E would. It's probably a good idea to install one since the exhaust will run quite close to it when you install the turbo. I took the shielding off my donor 240D, to put in my 280CE the mouldings for the screws were already there, I just had to drill a small hole.