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.