Easily a 2.3T motor (duh) or a 302. I'd lean towards the 2.3l turbo motor only for ease of install compared to a V8.

But you know what they say, you can do whatever you want to your car with the only limit being your wallet. I imagine you could put a 502 Merlin in a Ranger. Expensive? Yes. Practical? Maybe not. Traction? Definately not.