Have you guys considered this?
http://www.supertrapp.com/product_se...t.asp?CatID=35
light, compact, small, about 18"overall, tuneable by the amount of disc/diffusers used.
fewer discs used adds back pressure and noise reduction. More discs added = loud and horsepower. Means your able to adjust for less than optimal lead pipes or to suit your riding conditions.
Forestry approved spark arresting and a simple slip on installation.