Rear diff bushings torn what to replace with?

[svxsubaru1]

This past week when i replaced my 5spd with another one about a week ago (destroyed the original) and I noticed, while jacking up the car that the rear diff bushings that the studs go into to from the rear diff were both completely torn. I was wondering if its possible to replace them with some stiffer stronger ones that wont rip from some abuse, how hard it would be to change, if any one else has had this problem, and could the ripped bushings cause a slight vibration under heavy load from the drive shaft area because of more deflection from the broken bushings? Thanks