1996 Dodge Caravan Engine clatter noise

Today I removed the intake manifold plenum on my 96 Caravan with a 3.3. With 149,000 miles.I wanted to finish a compression test on the back 3 cylinders. All three plugs look like the were never changed but they must have been at least once because the were Autolites ! The plugs were obviously in for a long time because the electrode was very thin to give you an idea gap was about.080 Compression test came out higher than the front bank by about 25 pounds. Removed valve cover and as I pulled it off I bumped it and heard the wonderful sound of clatter! The noise has been found! All of the rockers were worn out severe wear through the shaft! I bought this van (a southern gem)a couple days ago at a very fair price with the noise hoping for a simple fix like a broken valve spring, bent pushrod, or badly worn rocker. I am happy to have found the noisemakers way up top on this 3.3. I am wondering though, why the failure? No broken towers here. Evidence of some sludge but nothing major. I blew through the pushrods to make sure they were clear. What do you think? I am going to put the new shaft and rockers on tomorrow even though there is some wear on the tops of the valves from the rockers riding funny, Good Lord Willing! I am replacing the push rods to help compensate for the wear on the valves. I figure that new rockers and pushrods should help to close the gap. What do you think about this economy fix? And what would the root cause likely be? Gary