A couple of years ago I bought a old frozen up 460 out of a junkyard. The engine was rusted up on four of the eight bores. I soaked the cylinders for about a week and beat the pistons out destroying them. I then took it to a machine shop and asked them is the block worth saving. He looked at it and said it would need a minimum of .060 overbore or more, but wouldn't be sure until he tanked it. I told him to tank it and bore out the worst one and take it from there. One week later I stopped back in and had a pleasant surprise, my block only needed .030 to clean out all the pits. The only way to tell is to take it to a machine shop after you get the pistons out and have them tank it and inspect it. You never know, you might get lucky and it might need only a .030 overbore.