As far as width, that is up to you:
- http://www.4crawler.com/4x4/ForSale/Shims.shtml#FAQ2

2" works fine, your springs are 2-3/8" wide and if it'll bother you to see the narrower block under them, then get the custom width shims to match your springs.

Pressed in center pin means you do not have to take apart your spring pack to install the block as you would with a bolt-on block. For that, you'll probably need a longer center bolt for your spring (unless you have 3/4" or more exposed thread on your existing center bolts):
http://www.4crawler.com/4x4/ForSale/Shims.shtml#CenterBolts

On the u-bolts, grab a ruler or tape measure and check your truck. If your truck has at least 3/4" of exposed threads on the u-bolts and they are in decent shape, then you'll be able to re-use them with the lift blocks. If you have less than 3/4" of exposed thread, then you'll need new u-bolts.