Once both units are standing on their own four feet, its time to stabilize the legs. Once again, we'll begin with the 49-inch assembly.
Cut two 49-inch pieces from two 2x4's. (Save the cutoffs, as they'll be used in another step.)
Using the tape measure, place a mark 10 inches up each of the four legs on their outsides. Square the mark using the Layout Square.
Attach one of the two cut pieces to the two legs on one side of the assembly, aligning them just on top of the square marks and with the ends of the boards flush with the sides of the legs, as displayed in the image above. Repeat on the other side. Two screws at each connection will suffice.