Braking deteriorates and car look hideous. What I did was, I took the spacers to a Machine Shop where I paid him extra to reduce the height by 0.5 inches on both, in-fact made it half to that of its original size. Remember, spacers available in Market have size equivalent to 1.5 inches which you can measure using vernier caliper.
I am missing the first part, initially I installed the full size spacers but I did not like the look of lifted vehicle and braking became so bad that I started hating it within a week time.
Going back to first part, once It was done, Height of Vehicle looked almost same as once it was without CNG kit. I took the vehicle for alignment where alignment guy refused to do anything with back wheels. Once, I told him about the procedure then he said that it is then compulsory. Cambers were out which was corrected and eventually braking was as good as it was before.
Hope, this experience will help you out.