I have the Mustang's Plus kit on my '66. Upgraded to the 5 leafs (mid-eye) and KYBs (slightly rough ride, but not too bad). In addition, I cut 3/4 coil off the 620s and added a 1" lowering block to the rear. This gave it a slight rake to the front, but it sounds like every Mustang differs slightly. And never scraped my tri-Ys yet.
Even though I have a good-bad relationship with Mustang's Plus, it convenient to purchase their products on eBay (cheaper than there catalog price) and pick them up locally (I work down the street from them).