I don't particularly care for the Gabriels, either and prefer the Monroes. If your dad works on cars at all, he shouldn't have any problem replacing the rear shocks. They're the easiest that I have ever done.
I just replaced my rear shocks with the Monroes about two weeks ago. Since they are shocks, there is nothing that will change the alignment by changing them. I am quite happy with the results. It took about an hour per side and was very straightforward.