They aren't too bad:
1) Support the rear sight block with the old retainer "handle" facing down. I used the jaws of a bench vise, opened up jsut enough for the handle to clear. Make sure there is room for it to drop out.
2) Get a punch that will fit just inside the dimple on the broken retainer.
3) Tap the old retainer out. It won't take a lot out mussel, so start lightly.
4) Put the new one all the way through the sight block. You may need to tap it through with a hammer.
5) Support the new retainer on the handle side. You want the solid pin part to take all the pressure for the next step. Take care that the handle is clear or it will break.
6) Flare the other end of the retainer with a hammer and punch. Go slow and check it a few times, rotating the handle, so it won't get super tight. Also check for play back and forth.
It really helps to have an extra pair of hands when doing the above. Have some one hold it steady while you do the work. You will have to refinish the side you flare. Cold bluing usually does it. Just take your timeand you will be fine.
Mike