I have a mustang 2 clip under my car and a 351w ready to go in and am still having header questions. On this board I have seen the guy use bbk 351w swap headers in an ls1 maverick with a mustang 2 clip and had plenty of room. An ls1 is a little wider than a 351w. I have also seen the same headers work on a 65 mustang with a mustang 2 clip and a 351w. I plan on buying these headers soon but want to see if anyone knows if they will work. I believe they will. Here is a link to the headers http://www.summitracing.com/parts/BBK-1569/?rtype=10
It was a big jump to go buy them not knowing! If they don't fit exactly right there's always the option to cut the flanges off, rotate the tubes to where they do fit, and re-weld them. Sadly, BBK doesn't offer them in bare steel...