My first build was an OI... hard to beat for speed and directional stability, rock-solid secondary stability and leaned over it turned very well No skeg needed, but in a very stiff crosswind it would leecock a little. A couple of my friends modified the design in the way you suggest. One enlarged the plans about 7% then added about 2" of rocker in the stern, but he built it around a composite based on boatbuilder's foam (Corecell or something like that) with alot of Kevlar in the layup... great boat, bombproof literally, but weighed in over 70#... he no longer has it. The other took a sawzall to an Impex OI, removed a couple of inches from the keel aft of the skeg... still has the boat and loves it. Many ways to skin a cat....