If'n you are building a model airplane to fly - not just looking for wind tunnel guestimates -- be forwarned.
The airflow just behind the prop and whre the cowlis close,is a real problem
You have either a stagnant flow OR the flow is winding and air into the cowl will cool better on one side then the other .
How do I know?
I measured the heads and plugs with a pyrometer , then cut holes in the cowl to change airflow .
Our models engines do not have the benefit of good ductwork to force air thru the fins -so overheating a twin is a reall issue - even a single needs good flow into and if possible forced to flow thru the fins.
On 100-200 CC gasoline engines this can spell life or death of the engine.
The size you are working with suggests you are using a small glow engine of perhaps .40/.60 cu in.
Look at control line speed models or FAI RC speed models and get some feedback on "pressure cowls ".
done right - you can make a very small inlet with an extractor outlet and on the very rich oil/alky mix not cook the engine
Get er dun!