The forums I belong to have very little information in English...but if you hold your mouse over the buttons - the status area of the browser should have English terms for the functions.
Yeah - there are always '98 - '99 E300 turbo diesels on eBay, Autotrader, etc. It's a ~$10-20,000 used car depending on mileage, condition.
The OEM injection pump is electronically controlled and the newer ones use CANBUS to control the injection pump. "Superturbo" cars use a mechanical injection pump...so you're going to loose your cruise control, possibly some HVAC functions, possibly the alternator charging circuit, the automatic tranny won't know how to shift, etc.
Yes - the 5spd automatic is all electronic...but the good news is that this transmission is also behind the Hemi V8's in the Dodge Chargers........so - you can see where I'm going with this......the modifications those guys do to their automatics will also work on one in an E300.
An NA OM606 found in an earlier (non W210 chassis) car would also work, but you'd be better off finding a turbo'd unit to start with since the hard parts are already setup for the punishment.
Some guys have used Mercedes manual trannies behind these, but they claim to have a very hard time keeping clutches in them. They need to get in touch with Peter at South Bend Clutch...or just adapt them to a beefy American tranny. Our friends in Sweden have put TH350's and TH400's behind some interesting engines. Here in the US - TH400's (and 4L80-E's) have been known to be found behind more than a few modified Toyota 2JZ-GTE's. Sound Performance in IL innovated this - here's their Stage I kit:
http://www.spracingonline.com/store/SP400_Transmission_Stage_1/21
They basically cut the bellhousing off a core TH400 and bolt up a new specially modified plate to the front pump area that allows you to use a Toyota bellhousing bolted to that. This setup has held up very well in race/street applications - something to think about.
I was thinking of maybe even using a V16x (6-speed) out of a MKIV Toyota Supra...those trannies can put up with a LOT of abuse and you can even buy a $5k (totally rebuildable) racing clutch (carbon/kevlar?) that'll take 1400hp....
Cheers,
Matt