Mike , the slot is vertical. I compared it to another SM420 I have and it looks correct. I have bumped the shaft and it does not move. Looks like some fun is about to happen.
The shop manual says "Horizontal", which would put the slot in line with the pin.
I just went out and checked (4) different SM-420's I have and none of them have a slot in the shaft, so I have no idea how they lined it up when new...
Here's a picture of one of them.
Mike B
