This is what I used to replace my Williams front sight with a Williams firesight. I went slowly and carefully and it was not a problem. The front sight could be inserted or driven out from either side. The new sight did require just a bit of filing to make it fit the dovetail (Williams warns you that you might have to do that.). Make sure you use or make a file with at least one side with no teeth. (I bought a small triangular file and ground down one side using sandpaper on a glass flat plate and then a sharpening stone.

http://www.midwayusa.com/product/732798