Cast and Hyper pistons are made in Standard size as well as a 0.020", 0.030", 0.040", and 0.060" normal production overbore pistons that are sitting on the shelf awaiting your order. Forged pistons are on the shelf only as a 0.030" or a 0.060" over bore size. The piston companies will make pistons in any size you want (pro stock engine builders buy custom pistons in an over bore of 0.002" at a time and have for or five incremental increases in bore sets ready to drop into a block as it wears to maintain a tight seal.
As for as your 402 block it can be safely over bored 0.060" (and even then you should check it for core shift first). If while you are sonic checking the block you discover that the core shift for all eight pistons happens to fall onto the thrust side of the block you could take it out as far as 0.100" over and still not have a cylinder that shimmies as the piston moves down the bore due to deflection of a thin cylinder wall. A partial block fill helps the bottom of the bore stability with a motor over bore like that; but expect the block to run hot. It runs hot not because it is half full of concrete, but because the cylinder walls are so thin that they glow red from the cylinder heat escaping into the coolant because of thermal transport through the thinner cast iron. That lost heat, is lost power.
Big Dave
