it depends on what thermostat you are using, but that sounds right, seems like it will work just fine.
i get all my parts from partsexpress.com like the diagram said, i used 40 amp relays just to make sure they would handle it, i didn't know what amperage they pulled , but i know it's not only 40amps.
ya, there are two pins to use, on the switching side of the relay, simply have one pin going to one relay, and have the other pin from the pcm go to the other relay
i'm not sure what pins they are on the truck, i remember seeing blue 42 , red 43, chck to make sure,
do you have ls1edit, you'll need to adjust the temp settings, or i can do it for you very cheap.
i'll do some more searching on the pins.
later,
allen