On a M119 any generation the valve covers will be a bit ground-down. One can replace the critical three lower chain guides from the valve covers without ever removing the front cover. No need to open the whole thing up. You may have to remove the waterpump to do this as you need the chain guide puller tool. You will to replace the rubber waterpump seals if you are doing a 89-95 engine M119 replace the rubber elbow at the smog pump valve.
The two flat passenger side guides wear the most, and the upper driver guide has to be changed. The lower driver guide one has to pull the timing cover, and obviously the guides at the top of the heads are not the guides I'm talking about. those are super easy to do.
I watch my buddy do this half dozen times on his engines
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