Post a video of the truck running. If you have been driving it as-is, my gut says your motor is ok. If it is the chain guides, stop putting miles on that motor.

The cost and time associated with pulling the old and installing the new motor is well over $700. You still don't have any idea what condition that motor is in.

If you can't find the source of the noise then pull the head, assess the damage and go from there.

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2002 X5 4.6is - Titanium Silver / Black Alcantara - Dinan Stage 2 - Bilstein/Eibach - Brembo BBK ----SOLD---
1993 318i - Brilliantrot / Tan - bone stock daily driver