T-Man! Love your videos!
When I machine air filter adapters, I put 2 flutes in, for the holes you're talking about, but my adapters have the exact carb bore size at the mating surface. Looking at yours, you will be able to get away with just notching the hole on the lower right. The upper right hole, isn't necessary, iirc....( It is a vent? )Just notch the one, and run it.....
The paint cap is a cool idea! Shouldn't have any problems, as long as you use the right filter material. Maybe like the foam filters the sell for big briggs engines. Just pull the foam apart, and stuff it into your cap..... ?