I'm trying to remove the lower unit on my 1970 50HP Mercury. I've taken the prop off (don't know if that's necessary, and all bolts. I need the impeller replaced (water not cooling engine) So how does this lower unit come off. I read that many people had this same difficulty. I read that the LinkAGES need to come undone!? Where are they!? Can someone help please, thanks! (I'm looking for a manual, so I will get one real soon!)