How heavy of a rear are you needing? If you don't think that you need a full floater, you might consider the 14 bolt 9 1/2" ring gear from an '88 and up light 3/4 ton. Many of them have 3.42 or 3.73 gears and they can be had fairly cheaply. Most also have the 6 on 5 1/2" bolt pattern for the wheels. Stay away from the 4x4 version, it's too wide. On that '77 rear, it should be a leaf spring unit, the last trailing arm rear was '72.
