are you sure your plug wires are all on? do your 289 heads have adjustable or pedestal mount rockers I'm assuming adjustable and that being the case you will need to make sure all the adjustment nuts are tight but don't just start tightening them down you have to set them correctly if they are pedestal make sure the bolts are all tight although if they were loose you should probably be able to hear it at idle also.ok since you are a virgin at this when you take the valve covers off look at the rockers if there is a stud with a nut on it they are adjustable but if there is just a bolt head they are pedestal mount these should all be tight. try to move the rockers around by hand if the pushrod is down they will move a little not a whole lot but if any of them move alot you need to tighten them down
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