get ALL the injector seals and return line seals, don't try to reuse the old, (8 injector to return line, 2 return line to head seals, the chance for an internal leak is too great )
DRAIN the coolant before you pull any injectors, if you pull an injector cup you run the risk of filling up a cyl with coolant ( not good )
get a couple injector cup seals, you'll more than likely pull at least one ( red silicone rubber O ring seals , 2 per cup ) you'll also need some anerobic sealer for the cup to head seat.
I've got the GM tool to pull the LB7 injectors that I will sell ( $70 ) it can be done with out the tool, but it's so much easier with it ( and you don't risk messing up anything else ( the tool new sells for $90 ) if you've go some miles on the truck, more than likely there will be some carbon build up on the injector tip, which makes it harder to pull ( and more likely to pull cup and injector as a unit )
5mm ball end allen socket is your best friend on this job for the valve cover ( upper and lower ) bolts.
17MM wrench for the FICM cooler lines and injector lines,
8mm socket for the injector power wires ( be very careful tightening these, they are soft copper threads on the injector, and break easily )
10mm allen socket for the injector hold down yokes. 10mm socket for fuel return line to head bolts,
10 and 12mm for most of the junk covering valve covers and the air bleed in T-stat housing.
fuel line disconnect tool ( 2 sizes )
been 6yrs since I did an injector swap on an LB7, I'm sure I'm missing a few details