Re: 71 Fuel Line to Engine Connection
are you talking about the connectors for a removable fuel line? I had a similar puzzlement: the pin on the motor was large, and fit only the old female fitting; I couldn't find a fitting with a large enough hole. even drilled one out. After few years I was looking hard at it and saw that the "large" pin actually was standard, and had the inner brass sleeve from the old connector stuck on it! The large female hole was so b/c its sleeve was gone.
I recall, when shopping for connectors, that OMC makes two sizes, one for smaller motors/fuel lines and one for larger, so an "OMC" package still might be incorrect.
Here's another possibility: the motor has been altered. At our hunt club when we all had OMC's except one Yamaha, we put an OMC male fitting on the motor so we could use any gas line. I have also made converters: a Yamaha female on 3" hose to OMC male. I also carry a Yam and an OMC fittings, both genders, in my tool box. You never know.