The AC unit goes in the aft cabin rear foot locker. The space will accommodate a 5000-6000 BTU unit. I'm not sure you will get a larger unit to fit. A water pump and plumbing goes in the engine compartment. The most likely units are MarineAire, CruiseAir, etc. that are a rectangular profile. I'm not sure the Webasto units that are more square will fit. If you install it, the parts will probably run approximately $2000.
Have a look at
http://www.boat-project.com. The second item in the section marked "Mechanical Boat Projects" covers an AC installation. Also, do a search on this site for others that have installed a system. There are several projects on this site that may be of interest. Most of these projects were done 8-10 years ago, and some may have more technologically advanced options today, but you can get a good idea what is in your boat.
A cheaper method, that is usually in the way, is to use a household 5000-6000 BTU window AC unit in the cabin doorway with a thick blanket clipped to the handrail on the upper door so it hangs down to the top of the AC unit.