The 96-97 OM606 had an ECU that could vary the amount of fuel injected at the IP - I'm pretty sure if you are going to get a 96 or later engine you are going to have to get the WCU and its associated wiring harness.

E300D engines are hard to find - PGA had a couple in stock several months ago and as I recall they were asking 3-4K dollars for one.