No, it's not difficult. I'm sure Dave has the pictures to show you?.
1. Jack up the car with the jack under the Diff.
2. Place stands under the rear jacking points under the sills.
3. Slacken and remove the nut and bolt which goes through the centre of the bush.
4. Lower the jack until the bush mounting aperture is below the mounting brackets.
5. Poke out the old centre part of the bush. (they are usually totally tired and fall out).
6. You then have to remove the old steel outer shell of the bush by cutting right through it in one place, then knocking it out with hammer and chisel.
7. Make sure there are no bumps or burrs in the alloy and assemble poly-bush.
8. Jack Diff. back up into position and replace and tighten nut and bolt.
9. Take weight of car on jack and remove stands from jacking points and lower car back to the ground.
10. Job done. Tea and road test (in no particular order)
Tony.