In my personal experience, it was always easier to just take your old calipers to Advance Auto Parts or O'Reilleys and get new ones. After the core charge, they weren't too much. I think I bought some one time that, after the core charge, were less than $40/each...
Generally a rebuild kit is no more than the o-ring that goes around the piston and the boot that keeps dust from contaminating the piston/cylinder. Sometimes the kit will come with a new piston. It doesnt take much to rebuid one.
Remove the caliper
Blow air into the caliper (be careful, the pressure will build, then the piston will "shoot" out)
Once the piston is out, remove the old oring and use some light grit sand paper to polish it up (assuming a new one isnt included)
clean up the bore of the caliper with a brake hone (if it is pitted bad you will need a new caliper)
install new oring and push the piston back in (keep it square or it will wedge itself in)
install the new boot, it should just pop into the groove on the piston and press into the caliper.
enjoy your rebuilt caliper that just cost you less than 20 bucks
the only thing i have to add is when putting the piston back in to becarful not to nic or cut the o ring pitting it back in. plum is spot on with the rebuild have done it a few times on other trucks its not to hard at all.