For what it worth, I bought a used stainless SX Powerbomb to replace my bent stock header. I noticed a rattling sound after installing it. The "pre muffler" had come loose with in the bulge of the header. (I later found that the spot welds holding it in place had broken all the way through and had to spot weld the cracks from the outside.) Not wanting any more down time I, used a pair of welding gloves, MAP gas torch and a pair of large angled needle nose pliers to bend and twist the "pre muffler" contents out of the header. The inside was very similar to the core of the muffler with even spaced small holes. There was no packing around it but there was a steel wool like material that was being burned off. It was pretty hard and falling apart at this point from heat, exhaust, unburned fuel, etc... I put the header back on the the bike an have been running for 10 months now. I found that the bike is less prone to stalling with the Powerbomb header versus the stock header. More so after removing the insides. It also seems happier being lugged if I blow turn and down shift down. I don't know if it hurt anything on top because rarely wind it out. I've only hit the limiter once since I owned it. I'd say you're in good shape building your own with what you're working with. Measure the distances of the bulge from the head on both the MX and SX versions and put yours in between.