From what i have read and gathered the Explorer 5.0 is a very good
doner. due to the shortened front end package(water pump, timing cover.
Also just a note, the explorer 5.0l has GT-40p heads and intake

I have robbed these heads before and put them on some of my mustangs
they are a good flowing head. Also as Mac mentioned the exhaust can
be a problem. the gt-40p spark plugs point strait out insead of angled.
so either you will have to keep the choked manifolds or by headers for
these heads. The only place I have found them is Ford Motorsports.
I think there around 260.00. One other thing, if you are going to be 4wheel
drive, all v8 Explorers are AWD ( there is a viscous coupling in the transfer
case to deliver torque the front wheels when one wheel slips.)
with that in mind it could get a little tricky due to that part of the
system going through the ABS module.