Sounds like you found a knee pad (clymer or seloc manual)... Better to stick to the factory manual...
In the case of a 1987 '470' engine (make sure it is a 1987
engine as it can be a different year engine than boat), the correct manual for the engine is #8, and for the drive #6...
You can find good used manuals on fleabay, CL, etc, or you might find a PDF one online that violates copyright.
Chris...
or PM me.