I know this thread is a few years old but I just wanted to add to the info contained rather than start a whole new one.
Here is an example of how NOT to modify your final drive pivot bushes.
Some previous owner had removed the needle bearings and pressed two bronze bushes into the needle bearing cups, relying on the anodised aluminium stub on the pivot bolt to act as the internal part of the bearing. Might have been ok when it was done but over time it has caused galvanic action between the dissimilar metals and eroded away the aluminium part. This has caused the pair to seize together and this morning the end sheared off, which in turn caused the other side (which had not yet corroded but was on it's way) to also snap off leaving me with a floating rear hub.
Thankfully I was not moving fast and managed to limp home. The failure and subsequent slow ride home has pushed the bronze bush through he back of the bearing cup so now I need new pivot bolts, new bearings and new bearing cups both sides of the hub and I'm lucky not to have had a serious accident.