Welcome to ribnet!
My engine is of a similar vintage, and so I am now well aware that Yam manuals for that age of engine are like the proverbial rocking horse poo. Thankfully, they sold lots of engines to Mariner, for which Clymer does a manual!
It's a bit "haynes-esque in that it seems to tell you in great detail what you can probably work out yourself, but it's better than nowt, and does have al the useful torque / sizing specs you may need.
Dare I ask what the problem is?