You might want to give Green Bay Propeller a call.  They have a whole warehouse full of old boat and outboard parts.     (920) 662-7605     14482 Velp Ave.  Suamico WI.  Just off 141 north of Green Bay.  They will also ship parts if you are not in the area.

Totally agree with once bitten, check.out that site and it should help you. I checked it myself and I am a mechanic by trade , the fact you can see the 3.0 on the valve cover is huge . I saw four models of 3.0 litre engines on that site , so I would definitely look there.  What you could also do is remove that alternator and take it to a local rebuilder and have they freshen it for you . There will be one somewhere in your area . And then figure out belt length . 

i’m still complety lost not even sure what engine in it can’t read mod number 

MarineEngine.com

Helped me every time I needed it