I know this is a silly question....but what size (diameter) is the header pipe where it enters the muffler on a XR650R? I don't have a 650 so i can't measure it. Why do I ask? I have the opportunity to buy a White bros E series muffler (brand new) for almost nothing, but want to fit it to my '87 XR600. Moving muffler mounts/cutting connecting pipe is no big deal, and it would be a bit simplier if the header pipe was the same as my XR600. Thanks.