More Horsepower wanted

I was wondering on ways to get more power out of my explorer. I have a 1999 xlt 4.0l sohc. I wanted a supercharger but i didnt find anything out there. Would i have to swap in a v8, and if i had too would i have to swap out the tranny as well. I was also thinking about a crate engine I don't know if it would be possible. I just want something, anything.