stall speed?

Cast crank 340's were built about mid 72 thru 73 . They are externally balanced with a wide funny lookin' balancer and use a weighted converter. Steel cranks use the thin balancer that looks like the one on a 318. Internal balance with the weighted converter will have a vibration. External balanced without weighted converter will vibrate. I never heard of a 340 from the factory with a 904.