Helping a friend look at a new truck

[Scoot5869]

So this Saturday I’m goin to look at a 2016 t800 with a cm2350 cummins. He is working on getting all the service records for it and so far we know
DPF and DOC filters were replaced at
615K miles in 9/22
#3 liner was leaking coolant and was replaced in April of 2023 at 662K Miles.
Rods and mains and a new clutch were done at 590K miles in June of 2022.

I’m curious as to why the rods and mains were replaced already, I thought maybe fuel pump went out? But if nothing else was replaced I figured in 70k miles something bad would have happened. The truck now has 664k on it. It is all stock still. Don’t need help with looking at stuff in the truck just what all we really need to look at on engine. How to tell if fuel pump has been changed if we don’t get service records. I don’t think we are goin to be able to get the valve cover pulled his shop is full and we are goin on Saturday just to look at it with salesman.
The truck was a tanker tanker in Maine. the purchaser bought another truck from same place same fleet a few years back and the truck has been great for him besides normal issues. It had the same amount of miles on the 2013 he bought so I’d assume they just roll them after so long.
Any suggestions would be great I plan on taking my laptop to hook insite up and see what pops up. So any ideas there would be helpful too.
Thanks