318 to 340

To seriously answer your question. You would have to get the block sonic tested to see if there is enough cylinder wall to overbore it that much. Your best chance would be a very early 318 block as they were cast close to the same as a 340 block. Or you could have the block cylinders sleeved and rebore but now your talking big money in machine work. It can be done but it really would not be worth the money.