How big are the rocks to what size tank and how dead, stink like low tide dead? If concerned put it in a 5 gal bucket, salt water from tank so do a water change, add a power head and do a few water changes to the bucket for a month or 2. Test water in bucket till cured. A large tank will handle the dead and bring it back to live in time. Remember the water changes.
Hmm..they are about 1-3 lbs each...pure white, not a schoche of life or stink in either.. They would be going in my 55g (I guess I should add that to my siggy eh? lol)
Do you already have rock in the 55 gallon?
If you have a significant amount of rock. I'd just toss them right in the tank.2 pieces of 3 lb. rock in a well cycled tank isn't going to do anything.