Hi Chris
According to the charts I’ve seen the D16 replaces the C7. That’s the recommended plug for the Ace and Handitwin.
Now watch the experts prove me wrong 🙂
I have used D16s with success to replace C7s, 13s, M5s and M6s. In New Hampshire spring/fall waters the D9 is too cold to replace M5s in most pre war motors.