I have used these parts dampers, rods (not the old skinny ones) and cranks (273 forged) with no issues in a 318 project with forged pistons. As far as I know the 340 forged crank is same forging, but the crankpins are drilled through to lighten them for correct balance with a neutral damper (same as 318) and the heavier 340 pistons. The cast 340 crank has an offset damper to compensate for the lighter crank material. I think you can mix 273/318 parts with no big issue, if using the 273 crank with 340 pistons I would say use the offset damper (And converter!) My Forgot to mention: Stay away from the 360 damper/converter for the 340 parts! There is way too much offset material on the 360, for 360 use only.