I used an 05' Grand Marquis 2V I got for $600 with 14k miles on it.
Parts I had to swap over from my old motor:
-Upper intake elbow and TB
-Oil Filter housing/lower radiator outlet
-Fuel rails and injectors
-Exhuast manifolds
-Motor mounts
Any 99-up 4.6L 2V (Truck, van, SUV, granny car, mustang) will almost be a direct replacement meaning you may have to swap a couple parts from your old motor. Winsors have an 8 bolt crank and Romeos have a 6 bolt. If you can't figure out which one you're looking at count the cam cover bolts. I chose an 03-up motor for the revised spark plug threads (8 threads vs. 4 threads.) I believe some 4.6L Explorers had aluminum blocks so that would be some free weight savings there. I'd suggest searching here that's how I found mine...
http://car-part.com/