Yes those tabs are the tangs, to keep the shells from rotating in the rod. There's tapered cutouts in the rod and cap for them. It's best to have the rods so the tangs are oriented to butt against the opposite part against the rotation of the crank, the tapered cutouts can flatten the tangs out and let the shells spin if the rods are the other way around.
Main bearings... you can't change the cases around, just put the shells in the right way.
I don't know if this is absolutely necessary or just a good practice.