Don,
If you have a 3 1/2" BC, go ahead and put it in there. Increase the horn height, also. This will give some help in slowing down the controls, and less stick force needed in the wind.
I do believe you can get a 4" in there witrh some minor alterations if you wanted to.
You can always increase line spacing at the handle for more response, if needed.
Of course, thousands of them have flown great with 3" BCs!
Bill <><