In my experience headers hitting the spring shackles is an almost guaranteed problem with front leaf sprung trucks, unless of course you're shelling out for a pricey pair.
In fact, on an old Wilsonette milk van my roommate is converting to a rat rod, he bought the hooker comps ($160 to our door) and simply made pie cuts at the 12 and 6 o'clock positions and bent the whole header tighter to the block to prevent this problem.
He then tigged the cuts shut and voila, perfect. Some high temp wrap looks good too, especially when dealing w non ceramic coated headers. It looks very racecar and at least you wont have old rusty headers under the hood like I do.