I was thinking of making something up out of stainless to replace that resonator, but really could not be bothered
All you'd need is about 500mm of 200diam tube, and two 200diam tube end caps. would need to weld a bit of 3" on for the plastic to grab onto when clamped on, or make the whole lots out of stainless and weld straight in.
then drill and tap a small hole for the sensor.
sounds easy and probably is, wouldnt cost more than $100 to make yourself, but who know if its going to help performance wise? its probably more wank factor.