You are definately going to have to go with a tranny swap since the ranger v6 is not going to handle the v8. If you go with a c6 you are going to have to do some major hammering to get it to fit the hump. Also, you will have some issues with clearance. I know of 2 people that stuffed one in their rangers. They raised their trucks and had nothing to worry about with the clearance.
Lowering your truck is easy there are a few ways to approach it and depends on HOW LOW you want to go with it.
Not sure about the rotary, but it is not impossible. You would more than likely have to fabricate some engine mounts, new wiring and replace the ecm. That is just for starters, not including the tranny..etc. But for overall power i would go with the v8 in your Ranger.