I have had a couple converted fridges. The first an antique with the freezer hanging down inside the second a top freezer. Very easy to drill a hole in the door and stick a shank through. Remember the tap handle may collide with the freezer door when you open it so plan on either going low or getting a short tap handle. With an old fashion or less expensive newer model with no fancy stuff plumbed through the door, drilling the hole should not be a problem. Use caution drilling anywhere there may be wiring, cooling lines or whatever.
With a set up like that you also get the freezer to store hops or whatever.
I have never had a chest freezer "keezer" but some of the pictures posted here of them look awesome. Right now I have a commercial kegorator that I got a deal on because it had a little ding in the side that had no affect on how it works. If it craps out I think I will be looking for a used upright fridge.