Lifters lose their prime under great spring force OR from lack of oil pressure. When they lose the prime they yell at the top of their ability!! Clicking and clacking till you shut off the engine. Nope! I'm fairly certain they were at top performance.
I'm thinking "someone" put some kind of oil additive in there with the oil.
Is it idling and running Ok now? Have you had it up and down the street?
After 30 or 40 miles change the oil and the filter again.. The diesel fuel that was left in there ain't doing your bearings any good. And YES there is some in there.
The camshaft in the 4.2 engine is not known to go away. If it now runs Ok I would leave well enough alone. A new cam might start an old engine to wear quickly from increased pressures.
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />