This kind of swap; regardless of which engine you use, will be VERY EXPENSIVE. The GM engines will not bolt in, and even if there is enough room in the engine compartment; you'll need custom motor mounts to support the engine, and a custom machined adapter plate for the motor to bolt to the transmission. You'll also need to adapt the vehicle wiring harness to the computer from the year and model engine you use (and it is illegal to install an older engine in an emission controlled vehicle) That alone will give you enough headaches to make it impractical. Even another Ford engine will require using the computer from the donor vehicle. And the exhaust system will have to be adapted to match the motor, exhaust manifolds, oxygen sensors, catalytic converter, etc.
However; the Ranger was available with an optional 4.0 liter OHV V-6 in 1993; and that motor was used through 2000. In 2001, the 4.0 V-6 was modernized and made into a SOHC motor; which was used through 2011. I'm sure that motor is lighter than the OHV motor; and it will have even more power. If you traded your truck in for a 2001 or newer Ranger with the 4.0 SOHC motor; you'd get al the benefits you're hoping for; without the hassles and cost of modifications. If you're curious about the fuel economy of those motors in different years; you can compare those figures at www.fueleconomy.gov/feg/download.shtml