You can't just "add" a turbo. The turbo version of the 606 motor had an intercooler as well. I beleive it was water-to-air. You'll need new exhaust manifold and I'm sure that many of the internals are different. I beleive the injection pump is different as well.

Maybe it would be more cost effective to trade in for a 1998 or 1999 E300 Turbo.