I should clarify myself on the 60-72 center section. There are a few vendors (and I mean a very few) that still have 4.11 or 3.90 gears available for the 3/4 ton rearend. Most likely they are used units. Anyhow, You need the 60-72 center section, they won't fit in the earlier ones. Like WBROWNE stated, the 67-72 automatic trans. trucks came with 4.11's from the factory. I've also seen online, some heavy truck salvage yards that claim to still have HO72 4.11 rearends. The price tag was pretty steep, starting around $700 and steadily going up.
