[Reiver]

The pitted cams/rockers are more than likely from the wrong oil not dirty oil...a guess would be a non zddp type oil. That's where you see the damage if the oil lacked zddp.
The lack of zddp will not cause an issue elsewhere...it's a cam/rocker specific ingredient for flat tappets.
With 58k on the motor I would not crack the case if in fact you find no other wear items in the heads (oil issues you mentioned).
Do you know any history as that helps with the decision on upper or total.
The crank/bearings/bottom on the 3.0/3.2 are known for their longevity....I'd only crack it if a known issue existed.