Check the oil level. I'm changing out an LLT with a new crate engine right now. No real warning just seemed to start knocking and then seized up. No oil in crankcase. I feel bad for you. It is however expensive no matter which way you go. We are doing the labor ourselves so saving that portion. But it's hours and hours of work even with the right tools and facility.
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No longer stock, but oooh so much more fun!

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