I simply prefer the more positive adjustment with the aftermarket plates. The factory rubber bushings in the top of the plates you currently have are most definitely worn and I would recommend replacing them if your budget so allows.
I recently installed these on my 87 along with new springs and struts. They went on easily and I had no complaints from my alignment guy on adjustments. They list separate sets for 79-89 and 90-93 but the price is the same.