Just because it has coils and an automatic, don't assume that it's a 4.10, though. My Dad had a '71 that had an auto, coil rear, but had the standard 4.57 gear. So make sure to check the #s, adn possibly do a manual check of the diff revolutions when you look at one.
One more thing, I have seen the Eaton diff with leaf springs in a '67-'72, mostly on 1 tons, and a couple of 4x4s. Seems that the Spicers were used more on GMC and the heavy dudty models, like the Camper Specials and tow truck packages.
