Hi, on my recently completed DR not so Big I had no room for the std airbox (due to shortening the subframe) so I obtained ( Ebay) a pair of 65mm bore K&N cone filters and mounted them on the battery carrier (as far from the carbs as possible) and connected them with the same bore alloy tube, with rubber sleeves. I was expecting set up problems, but I ended up raising both needles one notch, and going up in main jets from 120 in increments to 140 until it pulls cleanly on full throttle, and from tickover up. The only downside is the induction noise on hard acceleration. I also used a road legal Laser silencer, but the pepper pot in the outlet pipe was causing a restriction, so that went, making a noticable improvement in acceleration.
Dave