The Explorer is EEC-V OBD-II. So far we have 1 person on this site running it. By running I mean he started a couple years ago and got it to run but it has yet to leave the garage (as far as I know anyway). There is little support for that harness and computer, in art because it changed every 6 months so even going off years doesn't help. And early '97 is very different then a mid year '97 in both hardware and software. The mustang stuff stayed the same for many years and is very well understood and available. Go with the popular system and there are resources that can help you.
There are advantages to the OBDII system. Generally you have the computer and about half the wiring to go with it when you get the engine. Another is the local pep boys can read the codes with the plug in scanner. But there are other issues like what to do when you get the code for "fuel level circuit out of range" when not running any of the stock Explorer fuel level gauge system (and it is not compatable with the stock bronco gauge either). And if it is one of those with PATS (Ford passive chip in key security system) you could be in for a lot more wiring head scratching confusion trying to figure that out.
I would highly recomend doing the mustang harness and computer just to make life easy on yourself. Proven system that is known to work. If you want to be adventurious you could try the Explorer stuff, but I would recomend having a strong background in automotive EFI before starting.