I bought the diff bushing because I assumed it needed replaced. Biggu and I dropped the exhaust and had most the diff nearly out in around an hour before he noticed that it appeared to already have an aftermarket bushing already installed. Was in good shape, so it stayed. From what I understand the tool is designed to make it easier to remove the bushing from the diff. Apparently it is the worst part of the job.
I currently have Revshift motor mounts, Pacesetter headers (no cats), Magnaflo X. Revshift trans insert, CS diff bushing, 54 inch shifter, K&N CAI, and Brian tuned it.
It needs that carrier bearing bad. I'm getting some bad vibrations at freeway speed.
If the car you buy is stock I would do the motor mounts and shifter first.