If you are doing the JBA's I would go ahead and do the spacers as well, provided the back is at least 1/2" above the front now. Those spacers will raise you about 9/16" which, for me, put the front above the rear with only the OME HD all around until I added the Monroe F150 Load Levelers in the rear and balanced it out.

The JBA's should take care of the upper ball joint angles and prevent excessive wear.