The add-a-leaf kit was from pro-comp, I think I paid like $40 or so. However, an S-10 pack is probably a better idea, for the add a leaf you already have to remove the pack anyway. Might as well build a better riding spring than the AAL can provide you. I purchased 8 cyl. coils and would go a smaller spacer like 2" most folks avoid anything over 2" worth of poly spacing, just like an above post kinda hinted at. Some won't run spacers at all except the stock isolator/spacer. It can be dangerous if you flex alot, coils would be easier to pop out on you at the top. I don't have rocks to flex on here in FL.
That said, others are more knowledgeable than myself and may be able to help you more. Search around and an excellent link has been posted in here before on this exact lift. The bar pin on the explorer shocks has to be ground so that they are open on each end to accept the bolts at the top. The racing shock mounts are hard to find and supposed to welded in, but I simply drilled a hole in them to accept a bolt into the bayonet style attachment at the top and also at the bottom mount.