Watch out, the RX-7 engines are very low on torque, especially at lower RPMs. With the weight of a Ranger, it may not be the best swap.
Years back when I had a 1966 Porsche 911 (2250lbs), I had thought of swapping in a Mazda 20BTT 3-chamber twin turbo rotory from the Japanese Mazda Cosmo, but funds did not allow. Those engines can pump 500hp without breaking a sweat!
If you do this swap, I woul really recommend a 3-chamber, to give yourself a fighting change with torque to make it truly worth the effort.