That doesn't seem very likely as they show a picture of a 10 bladed impeller for th sb engine on page 7-6 of the fsm, and list it for not only the dart models but every Coronet model (excepting slant six) as well.
The interesting thing is that the 10 bladed impeller looks to be a cast unit with a flat across the back and a few holes running around the circumference of that plate verses the stamped steel impeller I have always seen.
