These drop in the stack and are 2-1/2" od. They aren't too expensive at $22 each. I think that is about what a decent screen will run now.
I have a picture of a 289 Cobra Comp Car with Webers with this type of screen on the stacks but temporarily lost it. When I find it I will post but they are similar to these Bug Screens.
Here's a picture of a '60s F1 car with screens over the stacks that run to the outer edges of the stack. The details aren't perfectly clear but that is a mechanical fuel injection system.
These are going to run with much less air flow restriction then the flat ones since the surface area is much larger.
