Earliest 340 production date/number

I was told that the very first A-body to carry or be carried by a 340 was a 67 Barracuda. That was on test grounds, spring of 67. He also said Plymouth dealerships received 340 S Barracudas before Dodge dealerships received 340 Darts.
This guy was a highly achieved master tech from a Dodge dealership in Cleveland Ohio. He liked to spout trivia, bring out old service bulletins, and such.
If he stated why they chose a Plymouth instead of a Dodge I don't remember ( was years ago ). Maybe location was a factor. We know Plymouth moved on to 318 and 340 while Dodge used up the remaining 273 engines lasting into early 69.