Ford F150 - 5.4 3 valve into a '97 4.6 4x4auto

First time poster here. I recently bought a '97 F150 4x4 xtra cab with a 4.6 auto. It is a higher miler with approx 145k miles. Although it gets good highway mileage of about 21 mpg(cc on at 60 mph)and passes air/smog check with flying colors, it just doesn't have a lot of bottom end especially when loaded with 15oo pounds.
I came across a newer(25k miles) 5.4 3 valve on Craigslist for what seems a great price.
Question is? How much of a swap is it to replace the'97 with the 4.6 to a 2003-07 5.4 3 valve. Yes it comes with the harness and ECU.

The 4.6 and 5.4 have different rear-ends. Not sure exactly what they are though. I also believe you need a different tranny for a 5.4 as well.

Anyone else got anything on this????
Any info would be appreciated, BCJake