I would keep it, you seem like u have a great pull dog, so I would replace the engine or simply have it rebuilt. No junkyard engine is my opinion, to many variables there. If u have access to a great engine rebuilder then I would go that route. If not then search out a quality factory rebuild from ford or another well known builder that carries an warranty. Good luck sorry to hear about the issue. On a side note I have never heard of the 6.8 having this issue before. I have always heard good things about the 5.4 and 6.8. Ford did a great job with those engines.