Check those things out, sometimes an engine can seem to run forever before needing a rebuild or replacement. Maybe get the oil analyzed and see if there is bearing matter in it but a visual inspection of the oil will show larger chunks as well.
And as far as the choice between the two, if you are a competent diesel builder with attention to details, have a strong torque wrench, have the patience to do things right, etc so forth and so on - then do it yourself. But if you don't know of a good machine shop, don't want to purchase the good parts or take the time to do it right, then just order up a new one. But either way, if you are going to have a new engine, then give it a freshly rebuilt and timed IP and injectors as well as GPs. It's all part of doing the job right.