It can be done, but it's definitely not a plug-and-play installation. Your best bet is to have the entire donor vehicle, as there are many things needed to complete the swap. All Explorer V8's are AWD (except 2WD versions) so you'll also need the transmission and center differential/t-case (or a manual t-case from an F150, probably a better choice) the V6 parts will not fit the V8 engine. The rear driveshaft of the ST is longer than the Explorer (longer wheelbase) so you'll have to get a longer rear driveshaft. Most if not all of the engine electronics (ECU and wiring) will have to use the '96's stuff. Probably nothing from the '03 will work with the '96 engine or transmission.
A 1996 is a Gen I and your ST is a Gen II (or maybe even considered a Gen III. I'm not sure). If I were going to attempt a V8 swap, I'd try to find as new of an Explorer (98-01) as a donor with as few miles as possible on it. The radiators for the V6 and V8 are also different, though you might be okay with a V6 radiator.
Doing a V8 swap and everything it involves is a pretty big job. It's doable and it's been done by several forum members. Perhaps they'll chime in on this thread.
