Differences between OM602 NA and OM602 Turbo, according to FSM (most differences also apply to OM603)
1. Turbo head is “reinforced at the water jacket due to higher combustion pressures.”
2. Turbo head prechamber bore is 15 mm, NA is 14 mm.
3. Original NA head gasket had normal sheet steel reinforcing around the combustion chambers (Turbo used stainless steel). However, all replacement gaskets are SS.
4. Turbo pistons have larger wrist pins (which presumably means different con rods), an annular oil channel for improved cooling, a recess on the piston skirt for the oil spray nozzle, a larger (18 mm vs 17 mm) prechamber recess in the piston crown, and possibly other differences depending on date of manufacture; FSM is not entirely clear.
5. Turbo engines have oil spray nozzles for improved piston cooling. Note: FSM section 18-045 says NA engine also have oil spray nozzles; this seems to contradict section 03-317.
6. The blocks may be different. I don’t know if all 602 blocks have holes for turbo oil feed and drain, with the NA blocks plugged, or if the NA blocks don’t even have those holes drilled.
7. FSM could be read as saying that NA 602 engines without EGR do not have oil coolers. (This may not be applicable to cars sold in the USA.)
8. Turbo engines have sodium-filled exhaust valves with chrome-plates stems and ground valve edges.
Source: “Service Manual/Diesel Engines 602, 603,” ©M-B North America 1991, part number LZ S-2517-091.