It is not a job I would recommend trying if you are a novice at working on diesel engines. The gear cover on the front of the engine has to come off just to get at the pump gears and bolts to remove the pump from the engine. You need to be able to bar the engine over to set the pump timeing after you reinstall the pump.
Why do you need to pull the pump in the first place? Unless it is faulty, any pump modifications can be done with the pump in place.
1998 3500 4x4 5 speed reg cab dually 12valve
TST #10, ATS exhaust man, 5" turbo back exhaust twin 5" stacks, SB 13.5 clutch, BHAF, DDP 75 hp injectors, 3000gsk, timing set at 16