Not trying to sound smart but it would be best to replace them with ones from another P38 :behindsofa:
You can get a turbo or pump off a 525tds, 325tds, omega 2.5 td but the P38 manifold is different so unless you're good with a welder try and get P38 one.
There is a subtle difference between the P38 and the 525tds pump (the most powerful of the replacement ones), not sure what exactly it is and no-one that has fitted one has reported feeling a difference but the P38 one is supposed to have lower peak power but better bottom end torque, we just don't know if this is solely down to the pump or fuel map. If it is the fuel map this will explain why no-one can tell the difference.