I would not get worried a lot with regard to the fin on the bottom, just seal it up so it doesn't leak. Ironically I welded up a lower unit just two days in the past. Dude hit a rock and punched a hole from the entrance of his unit, https://keylargoboatpartsaccessor75184.blogchaat.com/31551988/everything-about-mercruiser-lower-unit-repair