On your ProRock 80, there are 2 fill ports, one on the diff cover like you would always see and then another on the housing by the pinion. After re-installing your differential cover, you'll want to make sure you add oil at the pinion fill hole first - maybe about half a quart or so (this will ensure the proprietary pinion oiling system will have fluid in it) and then finish it up by using the fill hole on the diff cover. Remember, you just want to fill the diff until the fluid is at about at the base of the axle tubes or, up until it oozes out the weep hole if your diff cover came with one. You do NOT want to overfill the diff.
Your front ProRock 60 shouldn't have a pinion side fill port. If changes have been made since that I don't know about and it does come with one, you need to do the same there.
