ill admit, I am a total sterndrive noob. this is my first one, got it and the boat pretty cheap. it is a mercruiser 2.5, 1987 or close to that, but it needs an outdrive. I know it is probably an alpha one that I need, but is an alpha one an alpha one? or are there different gear ratios in the alpha one outdrives, and which particular one do I need? any help would be appreciated.