the problem with a used engine is you don't know about those lifters either (the lifter quits rolling and eats the cam, it is the lifter that goes bad and ruins the cam). I have seen them go bad as low as 100,000 miles even with good maintnance.

I would buy a 6.4 automatic cam, cost me $68 from dodge dealer ($109 cheaper than the actual 5.7 cam and a much better cam), a new set of valve springs $50 from dodge dealer or better yet the actual 6.4 springs are $200 ish and drop right in. A headgasket set from autozone is a couple hundred and check all the lifters by rolling them on a piece of glass to see if they are still rolling nice and smooth, replace any questionable ones.

The lifter and valve springs are the only consistant issue I have seen with the eagle 5.7, the short blocks and heads still look nearly new at 300,000 with good maintnance. I seen one broken rod (and 2 bent ones in the same mordor) but it was hydrolocked running through a giant puddle.