I need to clarify something. It's probably too early and I haven't had my first cup of coffee yet.
When you say, "height", might you mean thick? That is, 'How thick can the filet be?" And, what part of the splashwell are you referring to? Finally, do you plan to build the splashwell just like Renn describes?
As I think about it (hard work
I should probably had a cup of coffee before attempting to write this), I'll bet you mean the place when the floor of the splashwell contacts the transom. So, your "height" means how high up the transom can you go before interfering with the outboard mounting holes. Do I now understand you correctly?