Agreed with above get a OMC shop manual. You can find them all over eBay. I'm a owner of the OMC and Clymers manuals the Clymers manual is about as useful as a dr sues book.
Look at the casting plug atop the block, over one of the heads. It's probably painted over, but should have the model and serial number. It's the model # you are looking for.
View attachment 229154Look at the casting plug atop the block, over one of the heads. It's probably painted over, but should have the model and serial number. It's the model # you are looking for.