Found this from brother rustyratrod
".....
Lots of mis info in this thread. I have had both the 273 forged crank and the 318 cast crank on the scales. The 273 forged crank is lighter. The one we had was about 3 pounds lighter. Also, the 273/early 318 rods are lighter by a long shot than the later 318/340/360 rods. Balanced my share of those too. Of course, all of this could require rebalancing, depending on which piston you use. Lastly, no need to worry about the lighter rod's strength. Mopar Performance offered a performance version of the 273 rods using the same forgings as factory, but with good rod bolts and balanced very closely. They are long discontinued, but they do pop up on Ebay from time to time and they sell for a high price, because people looking for them know what they are. I suspect you could make a 340 scream real good with the 273 crank, rods and some really light pistons. I wouldn't be skeered to run them at all."
