[supermileage]

I am part of a team creating a supermileage vehicle for a collegiate competition. For the competition we are given a Model 9 Briggs and Stratton engine. This is an L Head or Flat Head engine. We would like to convert this to a overhead valve and possibly an overhead cam engine. I was wondering if anyone has seen this done or has done this? Or if anyone had tips on how to do this? We would like to know if we need to make a custom head or if there is an existing head that we could adapt for this use. I would also like to hear tips and suggestions on other things we can do to improve our mileage. We have the carbon fiber aerodynamic body under control, but would like to hear other ways of improving efficiency.