if you go to a big block, you could either trade straight across,(340toBB) or sell the 340 and then buy the big block. BB should bolt slip right in. what year 340 is it? could be worth some $$$would it be easy to swap a bb would i just have to change mounts only maybe i can get the vin an someone can tell me we car had factory bc the emblem on the hood says 383 ran #'s on block an says 340