Note I didn't say that a 4.0SOHC swap was impossible.
on say... a 1995-up it's merely difficult.
On a 1994 and earlier you have the additional difficulty
of dealing with retrofitting the EEC5 EVAP system onto the truck.
Remotely possible on a 1993-1994 ranger, difficult to the point of insanity
on anything else.
Basically it's the poster child for that collection of jobs that can be
encapsulated by the phrase "If you've gotta ask, No."
BUT if you have the requisite Knowledge, Skills and Materials you'd just
friggin do it, not ask about it.
It's even worse than the classic "Can I convert my TIB 2wd Truck to TTB?"
Again, not impossible, infact for some people, not even particularly difficult.
As an example on my '87 Ranger the decision to convert to 4x4 was
a difficult decision to make. And that first torch cut was a "point of no return"
But the actual mechanical job of removing the I-beams and 2wd engine crossmember took me only about an hour
Grinding the bits of weld out of the way to put the 4x4 crossmember
in took another two. basically If I had been determined
(and not out of C25 MIG gas) I could have done it all in a single 8hour day.
But I wasn't feeling particularly rushed because at the time the engine
wasn't ready for installation (and as it turned out that engine was no
damned good anyway)
MY own engine swap was a 1993 Explorer engine, I had a complete
1993 Explorer and significant bits of another 1993 Explorer to work
with.
But since my Ranger is a 1987 my swap experience is essentially identical to what you are proposing.
To be honest getting the engine into the engine bay and bolted up
to everything is EASY. because the 4,0OHV was essentially designed
to bolt into an engine bay more or less designed for it (actually the
2.8/2.9)
the trick comes from knowing what else you need to go with it
On my truck I also had the 2.9 harness to hack up and make the drivers side connections go more smoothly and I managed to "hide" ALL the splicing
behind the windshield washer/coolant reservoir.
But I also swapped in the 1993 Explorer power distribution box
One complication from using 1993 wiring instead of 1990-1992 wiring is the 1993 Explorers all had ABS and decided that was impractical to install.
so all that wiring had to be removed.
It took me a couple days to strip the unnecissary wiring.
However the two relay sockets it freed up were convenient for my auxiliary
lighting relays.
I greatly complicated my swap by adding "tow wiring" (diode isolation and
relays so that my tail lights would work when my truck was being towed.)
cruise control and dual fuel tanks.
AD
Welcome Visitor! Please take a few seconds and 
Maybe someday, someone will offer me a beat up old explorer for $100. I know it happens. I hear of plenty of people finding those deals....I just wish it was me for once!! Lol.
