I'd run a CRF230 muffler if you could find something take off, or a TTR230 one. Have an adapter made or turned to line up. I used converted a 400ex muffler onto my daughters future 300ex cobra header. It worked out perfectly with a turned adapter piece welded to a cobra head pipe. If it flows a bit better that's cool. I do like stock mufflers now days...I dont need the sound to bang around in the woods with family and friends. I bet you can still buy new CRF230F mufflers for prob $200...that would be way better then spending that on a 40 year old 200x OEM muffler.