Ok, I am trying to order a lift block set for a friend he has 02 f150 4x4 and need to know what size to get. I want to crank the front about 2" and raise the back about 2" also. The problem comes in when I discovered that 4x4 trucks posibly have a stock lift block (2" I think correct me if this isn't so). This presents two options.

Option 1 . Get a 2" block and stack on top of or under stock block.
But will the kit come with long enough Ubolts and blocks designed for stacking?

Option 2 Get a 4" block and take out the stock block.
But will the kit come with too long of u-bolts (not enough threads to tighten) and will the blocks be designed to fit squarely on axles without stacking?

I'm looking to go Skyjacker if this matters.
Block And U-Bolt Kit - BUK2071 (2") or BUK3572 (3.5")

 

Stacking blocks is not the best idea. Some guys here have done it, but is is Not a recommended practice. As for the size of your friends current blocks, get him to crawl under there with a tape measure and measure them. You never really know the history of the truck anyway. The best solution is to check.

 

You can also do a AAL. Don't stack the blocks and confirm that he has factory 2" blocks.

 

Ok this is starting to be quite the debate now... Everyone says don't stack the blocks but yet Almost every kit I look up requires you to do so...

I asked fatboysgarage.com how their blocks were intended to be used and they replied that "they replace the factory blocks".
However clicking on the instructions posted on their site, I see that it says to "Place the new block, tapered end toward the front, between the stock block and the leaf pack. " While a picture shows it placed between factory block and axle. http://zoneoffroad.com/Instructions/F1212.pdf page 3, Line 5
So now these instructions contradict themselves on the exact placement but still indicate stacking.

I have also asked on some other forums and I keeping getting conflicting answers. Mostly everyone says don't stack the blocks. But then looking here: http://www.off-roadweb.com/features/.../photo_08.html A Pro Comp kit with stacked blocks...
I decided to look at some of the installation guides to the following kits.
Pro comp 6" kits stack the blocks. (Factory block goes on top)
So does Fabtech 6" kit with blocks. (Factory block goes on top)
So does skyjacker 6" kit with blocks. (Factory block goes on top)
Tuff Country kits however, replace the factory block. So thus it appears it can be done either way depending on the manufacturer.

I couldn't find the installation guide to the skyjacker BUK2071 kit anywhere so I called skyjacker and asked about it and they said that their blocks go under the factory block and u-bolts will be long enough for this setup. Hope this helps others who might get caught in this confusion.