I've replaced mine. Once on a dropped engine and another time with the engine in the car. It's very tight but can be done with the engine in the car. Not a project I would recommend a casual mechanic take on as you can easily screw up the engine timing.
Depending on which bank you do you should lock the engine at cylinder 1 intake stroke or cylinder 4 intake stroke. This will set the cams as such to not be loaded on any valves and make it easier to reinstall.
And there's a lot of "while you're in there" items that would be good to take care of. Spark plug tubes, chain guides, chain tensioners.
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99 3.4L
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