340 ballance

look behind the right engine mount. the casting date of your block can be found there. best wat to tell if its internaly or externaly is by the vibration dampener as already stated. IMO external balance is just stupid! i NEVER will rebuild a 340 with an external balanced crank (unless its a # match resto). i will use either the forged 340 crank or a 318 cast crank. either is internaly balanced and have the same demenshons, however the 318 crank is about 3 lbs lighter. in some racing applications 3lbs of rotating weight is huge.