Have any of you seen a 300 straight six outside of a truck? The block is ginormous and I'm pretty sure that engine weighs at least 3x as much as any ranger engine. You'd have to put the front suspension from a F150 in as well just to hold the stupid thing up.
That being said, I am a big fan of the 300/4.9L. I just don't think it belongs in a ranger - it's too long and heavy. The 4.0, as Will described, is a great engine for a ranger, and they really do have quite an impressive amount of torque down low where it counts. Going from a 2.8 or a 2.9 to a 4.0 is a huge upgrade in torque.
But you still can't compare a 4.0 and 300/4.9L when it comes to torque, and realistic things like what the truck feels comfortable towing. That's like comparing a pocket knife to an assault rifle. If you want a fair comparison when it comes to towing crap, the 300/4.9L, 351/5.8L, or the modular 5.4L are pretty similar as far as how much trailer they'll feel comfortable with. The 302/5.0L and modular 4.6L don't even measure up to the 300/4.9L with a trailer behind them.