just add the pieces that will work and dont add anything that wont.
Have a cold beer - lean back -close yer eyes and think of smoke coming into the front of the cowl - then imagine how you would add a little vacuum at rear of the cowl to pull the smoke thru the engine fins .
Re member-------
The air pressure in the cowl must always be lower than the pressure outside the cowl
If'n not ----- then there is no airflow.