By '72 some of the 3/4-ton trucks had Dana axles instead of the Eaton. Make sure you're getting gears for an Eaton if you order.
Also, if you find a place where you can order the 4.11 gears for an Eaton please make sure to post it here. I don't believe they are available new anywhere. Or at least none of the people I know who have looked have been able to come up with them.
