Take the wheel and spring washer off of the arbor first and then place the plate on a vice and do the jaws of the vice up to offer as much support as possible around the arbor but without any grip on it as you want it to pass through the jaws. You then hit down on the arbor so it passes through the brass lifting cam. It is a very tight friction fit and the ends of these arbors tend to be quite soft so it is easy to destroy the end on the thread when hitting the arbor. I would put the had nut back on so it is level and then place a hard piece of wood on top before you hit it. Dont go too hard on it, I find fast light taps will be enough.
In all honesty, if the pivot hole is not that bad then I would just clean around it as best you can and leave it at that. If you do miss hit it and ruin the thread it can be a pain to sort out, not to mention the fact that when you have bushed it you then have to hammer the lifting cam back on. I have made a brass punch to do this which is just a piece of brass rod with a hole deep enough to allow the arbor to move into as it pushes the cam back on the arbor. It is either supported in the vice or in a split stake. Dont forget to do this before you put the plates back together.
Hope that helps,
Paul.
