Ive got a customer's fx400 quad with an Hmf exhaust on it and I wanted to get a quiet core for it. Is there any difference between the Hmf slipon and full systems. I cant tell if if the fx400 header is stock or not.There are no ID tags on this one for ordering the core. Couldn't get through to HMF today. Does anyone have one they might want to get rid of?Just the Core I mean.