247K Mile LS puts down 1500+HPIn this article they tear down a 247K mile iron block 6.0 clean it up gap the original rings and then get over 500 hp naturally aspirated and then push it to over 1,500hp with turbos before it slings a rod.
I wouldn't worry too much about the mileage on that motor until you start having real problems. How's the oil consumption? Any extra valvetrain noise? Might throw a compression gauge on there.
I do a coolant replacement, regular oil/filter changes, a can of seafoam, and fix any other little issue you can think of. Transmission is what I'd worry about more than anything at this mileage level.