By far, the easiest swap is a 3.0 V6 or 4.0 V6 from the same year 2WD Ranger as yours. 100% bolt-in and plug and play. You'll need the complete engine, engine/trans harness, engine bay harness, transmission, PCM, Y-pipe, radiator, overflow tank, electrical distribution box and a few other odds and ends. Also get the keys from the PCM donor or a Ford dealer will have to program the PCM to accept your current keys.
IMO, the gain in performance with the 3.0 V6 is not worth the effort. If you swap in a 4.0 V6 and intend to abuse it or tow, also plan on swapping in an 8.8" Ranger rear axle. Otherwise, the stock 7.5 axle from the 2.3 is adequate.
2003 FX4 Level II, Supercharged 5.0L V8, Headers,Duals 4R70W auto, BW4406 manual T/C
Aussie Locker, Torsen L/S, 4.10's, Bilstein 7100 rezzies, Cadillac/Mustang rear discs, Duff traction bars
Keypad Entry, Lock LEDs, ABS switch, sway bar discos, Heated seats, Explorer EATC, Trip Computer and consoles
5.0L V8 swap: Click
2003 XLT 2.3L M5OD-R1 reg cab beater, 2011 Taurus SEL, 2016 C-MAX Energi Plug-in Hybrid