On the bright side, the Explorer has more room inside to work with. If you do plan to tackle it yourself, it's not an easy task, which is why a lot of folks would rather ante up and spend the $800+ labour cost for a $60 heater core.
You're best bet is to do two things, besides the obvious and getting a GOOD tool set, is to get a repair manual (Chilton or Haynes will do), and check around online for a factory service manual (FSM) you might find a free version you can download. The FSM will better guide you through the process, as it's what the techs at shops use for reference (for the most part). I find the Haynes manual to be fairly thorough for the price ($25-30). And it's good for other maintenance and electrical items as well.
There are some FSMs on Download PDF PDFTown.com | Free Download PDF and eBook
and if you find one, it's all acrobat files inside a zipped file, and it's password protected, but don't fret, the password is 'pdftown.com'. I found one for my Taurus there, but I don't believe the link works anymore.
You don't need a lot of tech expertise, but it helps to know how to bleed the cooling system and fill it properly so you don't have any air gaps in the lines, which can lead to overheating. If you don't want to tackle it now, you can open the hood, remove the rubber lines going into the heater core at the firewall and tie them together. Of course, you won't have any interior heat doing that.
I replaced a heater core on an old Dodge Spirit years ago. Took me almost two days off and on to finish it. Say about 6hrs a day, or 12-13 hours total for a guy who really didn't know what he was doing at the time. Taking everything off was the easy part, it's the putting it all back and realizing I have ten extra screws was the problem. Good luck.