I loved the Aviator when it came out, but it didn't live long and not much could be done with them except a custom KB supercharger project.
Now that the newer engines are so much better, any of the latest Ford engines are great swaps for an earlier Ford, given labor, time, budget etc. I like the 2017 F150 3.7 NA engine for my 98 Mountaineer, some day.
But for the 3rd or 4th gen Explorers, any 5.0 would be a big upgrade, though those are very expensive now due to popularity. Those you're in the 350hp+ range, far better than the DOHC 4.6 of any model. The NA V6's are good choices if they don't have the internal water pump(never buy those). If they will fit in your vehicle, the price might be under $5k total, if you use a low enough mileage engine and trans that don't need rebuilding. I'm aiming for the 2017 F150 3.7, and a 6R80 trans of 2014+, and my stock AWD TC in my 98. If it works out, the fuel mileage will not be 19/20mpg on the highway, it should be well over 25mpg.