Haven't dropped in an Explorer engine, but I put in a 91 Thunderbird 5.0 in my GT. You will likely have to use the accessories off your original 5.0 motor, along with the wiring harnesses. I believe the intake is different but you can use yuor stock 5.0 one. And aren't those "P" heads? You'll have to buy aftermarket exhaust manifolds to fit.
I seem to remember reading that those that have done the swap recommend swapping the camshaft for a better one. I would guess the Explorer camshaft isn't optimal for a Mustang.
im finishing up the whole swap from a 2000 explorer.
get a nice cam, valve springs and seals. get and intake elbow or do the fox TB conversion. BBK longtubes w/ extensions and a mid pipe. Transfer the oil system and pan from your car. bolt up accessory's. 90 deg universal V8 wires. There is an oil elbow that is on the explorer block, i left it on and works fine for clearance... i don't have AC so i don't know if you keep it if it will fit, i still think it would to be honest.
You can read up on cobra cams that make good power, the one in my sig idles great even with an auto, then again i have my car tuned. If you don't want to tune it you can buy a stock cobra cam/rockers or use your stock cam from the GT... not really recommended.
A new upper/lower intake is do-able too for more power, up to you.
Im currently in the process of swapping in a 97 GT40P motor, with an eddy performer intake, and im going to try the ford racing "E" cam. the short block is the exact same as the mustang, so swap all the external acc parts over and you'll be golden. I do beleave the timing covers are the same, save for the crank angle boss that doesnt get in the way