I've got 2 K3's that use that number, also a 76 400F. The difference with the 400 is that there is the word TURN on the top of the switch over the left/right signal switch, I quess in case we didn't know what it was for!
That switch was used on the 73 models & forward, but not sure when the TURN was added and also not sure if the same switch was used until 78.
Nothing like confusing the issue.