What about the pan?

vintageracer
 
The 4.0 Explorer engine barely weights anything less than a small block Ford, and is even heavier than a small Ford with aluminum heads(450 or so pounds for each+-25 pounds). That is the main reason I gave up on putting a 3.2 SHO motor in mine(480 pounds). Also, the 4.o in the Explorer is known to have "issues" in reliability, fuel mileage and roughness, I would not recomend it. Better would be one of the later Ranger 3.0 v6 engines. They are based on the old 2.8 that was available in the Pinto and most of them are fuel injected. You'll only get about 170 hp stock, but just a cam change and tune would get you to 200. Another good choice would be any of the 2.5/3.0/3.5 v6 family from the Contour/Taurus, Cougar or Mazda 6s. They are all front wheel drive and would need work to convert them but they start at about 200 hp.
 
The perfect engine for a Pinto is a supercharged AJ 8 out of a Jaguar(4.2 400 hp). If you look at a side view of the oil pan area you will see that it looks designed to go over a crossmember in the same place as a Pinto's. The last Thunderbirds and the Lincoln LS have a normally aspirated version(3.9 290 hp), the Land Rover had a 4.4 version in both NA(300hp)and supercharged(450hp), though the oil pan would have to be changed.
 
Another engine would be the 3.4 v8 out of the late 90s SHO. It is an aluminum engine of about 235 hp and has the same bell housing pattern as all the Duratec v6s(thus the same problem of converting to rear wheel drive). You would have to fabricate an oil pan as well.
 
I have chosen to use a Rover V8(4.0 190 hp 250 ft lbs TORQUE)because it weights almost exactly what the 2.3 four weights(315 lbs)and puts out twice the hp and three times the torque in a very similar rev range! Rover was owned by Ford when the engine was made(technically making it a Ford engine)and I have both a 3.9(with a distributor)and a 4.0(wasted fire). You can also find 4.6 versions(or strokers to 5.0). Any of these can be stroked, cammed, tuned and ported to the 300+hp level and still be drivable in a very light car(Pintos are about the lightest at 2400 lbs), though it would have a NASTY idle. Not bad for an engine designed in 1958.
 
Grumpy