Slant 6 Split exhaust
All the pre-made options are pricey (Dutra Duals $750) and/or hard to source (Aussie). Some on ebay sell CNC'ed flat steel cut to bolt to the head. You add the tubes, which isn't easy, but some people are setup to bend pipe & weld. I recall the 1970's ads for motorcycle "4 into 1" exhausts, claiming 30% more power. When Honda and Kawasaki finally started making their bikes that way, the same places started selling "4 individual exhausts", claiming 30% more power. But people do say that headers waken up a slant on the top end, if combined with a breathing intake or turbo.