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Most overhauls you will see will need minimal work on the wear surfaces unless the engine has been severely abused. Modern chemical engineering makes rings practically not wear, to the point that running dry often wipes out a crank and rod, not the bore.
The only real wear issues on a properly maintained diesel will be; valve seats and valves, carbon buildup on valve stems, and soft items such as valve seals etc.
The main difference with diesels is the accommodation of the compression ratio. On IDI engines that run 23:1 give or take, the valve job can SIGNIFICANTLY change the compression ratio. DI engines such as the Cummins are much more forgiving as they are 16:1 (etc engine) or 16.5:1 (eth engine) so valve depth plays much less of a role in compression ratio.
However, valve face protrusion is still a major concern and worth careful measurement if you replace valves, and ESPECIALLY if you replace seats. This is mainly for preventing piston/valve contact, but is worth careful note. When determining course of action on the head, the fact that it is a DI engine may sway heavily towards minimizing work on the head. The main problem with valve/seat wear is difficulty starting the engine cold, but DI engines are MUCH MUCH more forgiving of being out of spec. IDI engines can be a NIGHTMARE to start if the valves are excessively worn. Most engines allow about .015" of wear to give you an idea.
I'm not sure about the Cummins, but all the IDI diesels I have cracked had multiple head gasket thicknesses to match compression accordingly. They were all IDI's though, so the Cummins MAY just have one. I dunno. Incidentally none so far has needed a complete overhaul, and some were SEVERELY abused.
If you don't do the head, I would encourage you to still pull the valves and clean the carbon off the stem/face as this will improve performance/efficiency measureably. You may be tempted to lap the valves, but if you do, go light. It's pretty easy to take them out of spec.
To summarize, the main difference in a diesel overhaul is the care regarding the valves and head.
PS, before ordering parts, I would consider taking measurements. IE ring end gap, plastiguage all the journals, and measure valve depth. You may be surprised.
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