The good thing about the 4.0 swap, is that it's entirely bolt-in since you could get a 4.0 in the Ranger. The bad news, is that the 3.0 and 4.0 share absolutley nothing, so you'd need to switch out everything that touches the engine (trans, exhaust, wiring harness, PCM, exhaust, MAF, etc). Basically, you'd need a complete 4.0 drivetrain or donor vehicle.