The inlet holes on the front of the cowl are probably adequate, just make the exit on the bottom a little larger than the combined area of the inlets. There are some allowances that have to be made, even in fine scale. The bottom opening is not readily apparent, but it's expected to be there, and the airflow will be across the engine that way. The side vents might look good, but the thin fiberglass of these cowls will only crack between the vents in a fairly short time from vibration and handling.