I believe that this unit comes with either a S6D 125 Series Engine or comes with a S6D 140 Series Engine. I have overhauled both of these style engines. The 140 Series engines are harder to get at the bottom end as they have a block extender. They are both individual cylinder head engines that are not as bad for blowing head gaskets. The 125 Series engine can last 25 to 35000 hours if taken care of well. That being said " These engines have very specific fuel timing done by fuel Spilling the Number 1 pump of injection pump."
I have done this process too many times to get bothered by but probably only 2 percent of the mechanics out there would know how.
Very often pulling the valve covers off of the 125 Series engine valve spacer assembly, the threads will all pull out stripped if it was not put together with lube on the bolts into Aluminum. Something this old may not have Wiring Harnesses available any more.
Unless they used the unit only 150HRS per year, I would say that the Hour meter has been changed many times. Don't be fooled by a hour meter. Insist on seeing the maintenance records. A fool is born every day, not saying you are one, but some people will sell pure junk to the unknowing.
Don't be scared to have a super competent mechanic check it over for you. Better waste $1000 for a quick inspection, than $75000 for a complete overhaul of engine at todays cost or even more. Tranmissions and pumps are big dollars. I have done a lot of work on same vintage WA 370 Loaders.
Komatsu parts are very expensive, and not a lot of people know that much about them versus Cat Loaders of the same era.
Hope this gives you some things to find out and consider.
Simon C