[big gear head]

The LT1 came from the factory with a 4.000 inch bore. If the block has not been bored oversize then you need pistons for a 4.000 inch bore. If the block has been bored oversize then you need to know how much it has been bored and get pistons to fit your bore size. If your block is worn and needs to be bored then you will need to talk with your machinest and figure out how much it needs to be bored and get pistons to fit after it has been bored.