What oil are you using? I'm not much of a 283 expert but if it's a flat tappet engine and you're using API-SM oil you could be experiencing excessive wear on the cam lobes. As they wear the lash increases. Just a thought.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.