If using an aircooled engine could you have less airflow through engine compartment for cooling if using a oil cooler? Us a thermostat so oil only flows through cooler when hot. Aircooled engines use oil instead of water to help cool the engine.
You would get a lot of cooling installing one like this but not the best placement for Aerodynamic purposes.
If you needed more cooling then that use an air scoop to get colder air into the engine or engine compartment. Also a setup like whats used for racing to bypass the muffler for controlling air flow through air scoop. Warmer air from engine compartment for start up and on cold days then cold air from scoop when up to temp and on hot days.