I had Outerwears make these TB covers for a TWM set up I'm building.
They had the patterns made originally for Kinsler Injection.
Took a week and was $89.95.
Many colors available.
Not as totally effective as a full-on air filter but these should filter out 99.5% of any harmful stuff on the way to your combustion chambers and have zero restricton on your intake tract.
HTH,
Mike
http://i294.photobucket.com/albums/m.../engjesel2.jpg