I'm not too informed on a flat plane crank, but as I understand it, it's basically 2- 4 cylinders mated together. I've heard the vibrations, etc can be brutal in one.

 

flat plane cranks are great for racing because of their natural ability to run very high rpm.

the coyote motor you are talking about is reported to make it's power in the 8,000 rpm range. great for racing, not so much for a truck.

also, without a balance shaft, the vibrations can be unnerving, despite it's natural ability to turn high rpm (due to smaller counter weights).

here's a decent video

and another:

my apologies for the off topic departure.
none of this has anything to do with fuel mileage while towing.

 

Mike, no need to apologize for drifting off topic of fuel mileage towing, imo. Where in the power band power is made has everything to do with towing. The lower in the power band power is made the better fuel mileage will be towing or not. Higher RPM means more fuel and air is needed to maintain proper A/F ratio. So therefore the fact that 180 degree cranks are made to wind high better than be a rock crawler is relevant.

 

I don't like the looks of them two inside pistons going at the same time. Just don't seem right. I have just exhausted my engine knowledge, wore me out.