Truck Repair: ISC 300 Engine, allison world, intake pipes

Question
I am interested in knowing how long to expect the initial engine to last before major rebuild. The engine is a Cummins ISC 300 HP (electronic ? ) teamed with a Allison World Trans B400. Original mileage on engine and trans in the 2000 blue bird Q bus is now 85K miles.

Thank you  

Answer
If they are properly maintained,I dont know.We never overhauled one because it finally wore out only because of dropped valves & dusted due to intake pipes loose(City buses).They have been out since 1997 or 1998.They do have liners so you can ovehaul in chasis if it is pretty open.