Quoted from John_I:

Yeah I did my Target Alpha in about an hour without removing the banks. I do remove the playfield from the game to make it much easier. As cheap as the drop targets are, I suggest using new ones. The old ones get brittle and will break if you are rebuilding flippers, etc. Also, there are two spring tools that are essential. Finally adjusting the switches and cleaning them is really important or the targets will be sluggish and may stick half way.
Try this:
http://www.papinball.com/tips/gottlieb_drop_target_guide.html