The Yamaha 6 I have is a 1998 model, 2 stroke so the cover is not as high as the 4 stroke is. I have looked at the 4 strokes, (there is a 9.9 on the boat one buoy over from me in the marina) and they look like they would fit fine though.

One additional thing to think about, I understand the only difference between the 6 and the 8 is the throttle travel limit,
it may well be the same on the 4 strokes.

Seems like someone here should have one (4 stroke) and be
able to give a more authoritative answer.