Here's the thing: your inbound Fox 2.0 Coilovers are able to adjust for up to 2" of front ride height, which should level your truck out dead-even, or even keep a tad of front rake, and this doesn't even take into consideration the variations between F150s, wheel and tire setups, and suspension wear and tear that can all effect ride height. Honestly, your best bet in this situation is to see where you're at once the Fox coilovers are on the truck and adjusted. If you still need a rear block afterwards, then you should give us a call a directly at 1-877-578-2433 so that we can find a rear block that works for you.
Back to your initial question, though: the ProRyde kit requires the removal of your stock rear block, and those height numbers are the amount of lift you get per ProRyde's block configuration. Depending on far you end up raking, you may need less than the minimum ProRyde block to even everything back out. While we don't have a 2.5" block, we do have 2" Blocks from Zone
that may fit your needs.