That's a sway bar. The bar you see in your first photo is a support - welded to the bottom of the center section and each axle tube. The torque from the driveshaft/pinion tries to twist the housing in the opposite direction, which can bend axle tubes. That brace helps prevent that.Okay but I thought they were like this! View attachment 1219189
On model car upside down, that is a factory Pan Hard bar, it laterally locates the rear end.Okay but I thought they were like this! View attachment 1219189
Likely an axle truss, too small and not attached to chassis both sides to be a sway bar.I saw this cool Chevelle in front of me tonight,and wondered about the bar that actually looks welded to the diff housing but is not a four link or sway bar(I think).What do you think?View attachment 1219112
Different bends also, that is why I said it was likely an axle truss, not a sway bar.That a looks different,larger diameter.