You do not need to buy the additional installation set when ou buy the 3.55 R&P set.
You could inspect the bearings/bushings/seals and see if any look like they need to be replace.
I used the installation set when I did the 3.55 conversions on to trucks, but I had the $$, and I did not want to go inside the rear-end again, and I was doing my work on a vehicle that will go to offspring.
I did not think that I needed new bearings and bushings, and they did not look bad, but after replacing them my already quiet truck became even more quiet at highway speeds.
