CM2250 fuel pump rebuild

[Truckdriven]

I bought a 2012 kenworth with 620k and want to rebuild the fuel pump because even though the entire fuel pump has been replaced I don't know what mileage. Do I need to replace the head assembly or only the barrel and plunger kits? Is there check valves built into the head that can fail? If they fail will they destroy the engine or simply not run properly? Lifters will also be replaced