In most cases on the 1st rebuild you can get away with a new piston and sleeve. In extreme cases or a 2nd/3rd rebuild you may need a connecting rod, crank and possibly bearings. At that point your better of just to buy a new engine(unless yor running a high end nova,RB,JP,Picco engine).

You can also go the route of have your piston squeezed by OSrocket off ebay or another place called rayaracing.. I think thats the name of his page.

Here is his web page.
http://www.acsu.buffalo.edu/~jfroth/pinch/home.htm

Ray