With the meet and greet out of the way, our story begins with how we bought this pair of unpopular diffs at the swap meet and our plan to merge their best parts into something we can use. The case on the left is a 489 packing 3.91:1 gears. As a Sure Grip unit, it’d be worth $500 to $700 all day long. But since it packs a street-unfriendly spool, demand plummets, and we scored it for $200. On the right is a weakling, small-pinion 741 case we got for $175. The object of desire is its Dana-Spicer Sure Grip unit. Most swap-meet buyers shun the 741 case; even in Sure Grip form, they fail to realize it shares the same Sure Grip unit as the rock-star 742 diff. By combining parts from these two orphans, we’ll come out ahead.