My uncle's 57 Custom had a 63 406 in it and ran a consistent 13.10 with the standard, down turn exhausts (I don't remember if he had the shortys or not). He built a set of headers that were swept up then down out the fenderwells (inner fenders removed of course) behind the tires and went 12.51. This was on the old, hard 7" slicks. With all this talk of modifying FE exhaust ports I'd think if one could back-cut the flange (take a small wedge out of the top) and tilt the flange back to allow the exhaust more upward travel before changing direction we'd be surprised by the results,
. On my uncle's 57 the headers came within an inch from the underside of the tops of the fenders. This kept the 'leaners' from spending too much time looking, "eww, ahh, ew, daamn",
, RodC