There are subtle differences between the Bonneville and Thruxton headers that result in a slight difference in the angle of the header outlets (where the mufflers clamp on). However, careful positioning and quality exhaust clamps will allow the dissimilar parts to fit together. The only difficulty is the centerstand/sidestand stop, which will not match up and requires an extension. Below is a shot of my '03 T100 with Thruxton mufflers installed. The clamp covers (available as a Triumph part) hide the junction of header and muffler...
