FYI, the 88660 headers are for a 351w. I've spoken with people who have installed them on a 289/302 and they will clear, but you can certainly expect them to hang lower.
that's not ok in my book.
I run the 88300 headers, and had to have tube #5 modified and relocated...the best bet is to have a proper set of headers and having the tube relocated.
If you have the mustang steve setup, run the 96+ sn95 adjustable cable, it's longer and will clear up top.
I now clear with an air gap down below, I taped the cable with reflective heat tape, then put a rubber hose over it, and used a spark plug heat shield over that, and it still doesn't touch. My cable effort is easy enough to depress the pedal with my hand, and I have no more heat soak issues with the cable.
http://slantnosefox.com/picturehosti...r%20welded.jpg http://slantnosefox.com/picturehosti...0shielding.jpg