I have a 1991 Thompson with a 4.3 Mercruiser & Alpha One outdrive. I'd like to know how to identify a Gen 1 vs Gen 2 outdrive. I had a 1988 Chaparral with 3.0 Alpha One, and they looked pretty much the same, at least on the outside at a glance. Are there any visual defining characteristics between them? Such as a boss or little detail here or there, elongated surface, serial number break, or anything like that?