Should be enough material there for a welder to make it work. The Alpha skeg is 9 1/2" x 5 1/4" and a Bravo I or III is 13" x 6", and a Bravo II is 13" x 7". The welder should just cut what he needs for the repair. But whenever i get mine fixed the welder has material on hand that he cuts to fit the repair. I never bring them anything to patch on.
I was thinking about getting a Skeg guard ? but wanted to see if it was same dimensions.. I guess not. What's the cheapest option for a guard ? For a alpha one drive ?
The cheapest option, as bondo says would probably be to drop the gear case, and take it to a shop and have a new piece of aluminum welded on. Change the impeller while you are at it and you should be good to go.