The stock cage is OK IF your carefull. Plus, it seals on the flat and the inner edge of the airboot, the Twin-Air does not. What I don't like is the airboot being used as a sealing surface, as its not flat. I would rather have an alloy plate that goes over the airboot surface, a little smaller ID with three locating notches for the stock cage pins. I'm sure it would be less than $120 and use stock filters. JMO. Maybe I'll make a proto this winter.