Hi Seaguy,
I run one of those "pod" filters on my single Mikuni, the one I have is from "Uni filters". They have a couple different types, some are just foam and some have a neoprene opening molded onto the end, and of course they are available in different lengths. The one I have on my bike is 6 inches long and extends back over my battery, which is possible because I removed the stock air filter backing plate long ago when I bought a K&N filter for the stock Amal carbs. In its place I fabbed a new backing plate from 1/8 inch aluminum (polished nicely) with top cut away for the filter. I don't know how foam or pleated paper/fabric compare flow wise, but oiled foam filters are standard equipment on most dirt bikes, are easily serviced, and relatively inexpensive.