Have seen these around. For many years. Mostly on competition machines. Use with 306 and later cases. Reportedly 20% cooling effect. Got one in my hands the other day.

Removed your starter ?

 

… no need to waste that space …

 

 

… fill it …

 

 

… with something like this …

 

 

… bolts in …

 

 

… filters with a big suck …

 

 

… through here …