Just wanted to say, it is going to be awfully cramped in that fridge with a CO2 cylinder and regulator, beer line, gas line, etc. Don't forget that there is a hump inside the fridge for the compressor, and it probably takes up 25% of the total volume of the cube in a fridge like that. You might not even be able to fit the corny itself in there even with the gas hardware on the outside. Especially if the cooling element is configured to be a freezer compartment, you will have some trouble.
We converted one of these:
with the intention of having 3 taps for 5L mini-kegs. We have two taps, and with a small CO2 cylinder (2.5lb, smallest I know of) and regulator, manifold, gas lines and beer lines it will barely fit those 3 mini-kegs comfortably (and they are a lot more maneuverable than a 2.5gal corny).
BTW, I recommend that above fridge for a conversion project like this. It is a little taller than the one you showed, but wouldn't be out of place on a countertop. The nice thing about it is that the cooling element is embedded in the ceiling and the freezer compartment is just created by an easily removeable insulation panel. With that removed it would have enough room for a small CO2 cylinder and one (or maybe even two) 2.5gal corny kegs. It won't fit a commercial sixtel though, and I doubt it would fit a 5gal corny keg. We got ours for something like $150 from Sears and shipping was only 7 bucks if you can believe that.