I haven't had the euphemistic pleasure of dealing with an Ecoboost, but I've taken the on-line training course for them. It's basically a regular 3.5 with hardened internals, modified heads, and a special cam.
The 3.5 is pretty big. A lot of services that used to be simple basic stuff now require dropping the engine out of the vehicle. You can't even change the front cover with the engine still in the car on the Edge or Fusion. Also, the peak width of the engine is pretty wide. I'm thinking probably wider than a 4.0, but I haven't been able to measure one properly. I would bet that putting an Ecoboost V6 into a Ranger would probably be similar to putting a 4.6 in a Ranger. Doable, but very tight fit. Also, I'm not aware of any current production rear-wheel drive transmissions that fit the 3.5.