The difference is the diameter of the main journals. The 273, 328, and 340 blocks have a 2.5" diameter main. The 360 blocks have a 2.81" diameter main. So no, you can't run a 340 crank in a 360 block. You can use a 360 crank in a 340 block, but you would have to turn the mains down to 2.5". If...