Per: http://www.mymopar.com/extcastnumb.htm
340 1969-70 Dart / Left 3614368
Perhaps a stock replacement?
That list has so much crappy info in it, it's not funny.
That's not even the correct number for that app listed.
3614368 LH 1972-74 A-body 340, 360
Yes with that casting date it's a 74 360 manifold, but, still same base as the earlier 340 piece..