i just received a 5521 injector pump for free from my brother that the bus company he works for replaced due to a bad pmd, i see this is the same pump that heath sells for all 94-2000 use, is there anything better about this pump vs the other numbers or is it just that it was the latest pump and that's why heath sells it?
i am not sure what my 98 currently has in it so i am weighing my options of what to rebuild to put on my new motor waiting on the stand

5521 has all the updates