Thats way too much money. A piston tapping the head? You mean tapping the valves? Or when the valve are closed the piston taps the head? I am kind of confused by this, if this was happening I would think something would be seriously destroyed to the point where it wouldnt run. Again how did you get come to this conclusion? If you are hearing a tapping are you sure it isnt a lifter or something? Like said before, go with the $700 short block from 50resto, you will have a block that is completely fresh, and you can reuse your top end, and maybe spend 100 bucks on gaskets at the most. Go to you local parts store and they should have a head gasket set for less then that, with everything you need for the heads and up. 900 is way to much for just that stuff. If you are going to tear the motor apart anyways, tear it apart and find out what your need FIRST before you start spending money.