Re: 1981 Johson 9.9 hp Looking DIY Skeg repair kit
The manufacturer can help you with the correct size for your LU.
I had a Johnson 50hp that had a damaged skeg when I bought it. I installed a Blackfin and never looked back. Make sure your old skeg is CLEAN! Sand all the paint and corrosion off of it. I'm not sure how much of the original skeg you have, mine was about 45% there and it needed to be straightened for the blackfin to fit correctly. Make sure you don't have a twist or bend, it will cause steering issues.
A blackfin isn't the best solution. Ideally you should have it repaired at a shop by a qualified aluminum welder.
P.S.
The adhesive that comes with the blackfin is very good stuff. You don't wanna get it on your hands, gas is the only thing I could get it off with....lol