Pete,
I made my own filters from 3 layers of household A/C filter media. The filters are held in place by a combination of a tight fit,vacuum, and finally stainless screen panels. I manufactured the gaskets from 1/4" vacuum hose, slit lengthwise, wrapped around the edge of the screen, and glued into the induction holes with black weatherstrip adhesive. If I ever get around to it, a turkey pan, sealed to the rear clip with weatherstrip, should completely seal the intake from any dust or foreign debris.
I have not had the car on a dyno since installing the filters, but I never noticed a difference.
If you have any questions, feel free to e-mail or PM me.
Bill