When you add the struts, you keep the rest of the suspension. The struts, springs (or coilovers if you choose), hubs, rotors, and brakes are what get replaced in the swap.
None of that is required. 280zx struts are already shorten than 510 struts. Then once you either install coilovers or decide to cut of the stock perch and weld it lower, you will get pretty damn low. Im only a few inches off the ground with 280zx struts...