Hello Grease:
First off, does the car have the HPP? Check tire size and look for dual exhaust. You will need handling to go with the new found power for a safe and balanced car, so make sure that the rest of the car is up to the engine's output.
Have you built any engines before? Do you have the tools needed to rebuild an engine? You will need, in addition to the usual hand tools, a complete set of accurate micrometers to check your machine shop's work, depth gauges and "straight" bars (many good brands, but think Lufkin or Starrett) and a recently calibrated torque wrench.
As for the engine, start by deciding what you are looking for. Do you want just a good block as a starting point for a complete rebuild, or a complete "good" running engine? Keep in mind that you need to change pistons, heads and cams, to get any power out of a 5.4. (The "bottom end" of a low mileage good 5.4 is more that stout enough for what you are going to build).
About this time, you also need to find a trusted machine shop in your area. Check with the guys and gals at the local drag strip or cruise night for a machine shop(s) they use and trust, and even then, check their work with the tools mentioned while you assemble the engine.
What I have said may seem complicated, but it is basic, and this is an easy swap, a real learning experience, and you will have fun and be very happy with the end result, so do not become discouraged! I was petrified when I fired up the first FORD flathead that I built, but I have gained much from that first engine in the years that have followed.
More to come, but get a copy of the latest Summit or JEG's catalog for reference, and get to know the people at the local speed shops!