I really don't think it matters whether it's a twin or a single, if your carb is too close to the cowl and the engine is running funny then a hole may help. I had a lot of problems when I first started flying my Bücker Jungmeister with a Sachs 4.2. I really hated to cut a hole because of the non scale appearance. Putting the hole for the carb fixed all of the funny running problems. The engine always ran fine on the ground.

Ken