I have been working on the airboat that my Stihl 25 CC engine will go on. My biggest question is how thick does the mounting plate need to be?

My design is rather simple, it will be a c channel shape, bolted into the starter holes. The flanges will be 1" long and secured to the pylons via 2 bolts on each side.

Is this design going to be strong enough? I've seen much nicer mounts on here and some sites, but my tools are pretty limited, and besides, I don't need it fancy, just functional.