Hello,
There were the Janspeed(from UK) conversion kits sold here in the early 80s, but none have survived, most have fried the turbo AND engine, nowadays the trend here is to stuff a OM601, 602 or 603 into any older diesel Benz, looked at a 200D fintail with a OM601 4 cylinder that the owner swears can get up to 170kmh(110mph). I try to keep to factory spec as far as possible!
All of this is done very haphazardly, with the engine out of line and cockeyed, cobbled up water hoses etc. And the scary part is that the RTD(our DMV) will inspect and PASS rubbish like this.
If I ever do a conversion, I would use a W126 280SE and stuff a OM602 5 cylinder turbo into it, early 126s now being worth very little around here and almost all were 4 speed manuals, always a good starting point, maybe even into my W115, for some reason I like the way the W114/115 cars drive, always found the W123s too soft and wallowy at speed.
For the time being, my week old(to me!)107 500SL keeps me amused. I need to remove the trunk lid badge, it is like a red flag to a bull among the ricer crowd around here!
Have a good week.

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Nachi11744