B) Not impossible just a lot of work. I would find a temp that your Weber will cook at and keep a consistent temp and adjust your cook time.
C) Use the Google search at the bottom of the page and search "snake". That is the easiest way to do a butt on a kettle grill. If that is not to your liking read the UDS thread and build one.
Team: Pyle's BBQ; Yoder YS640; Good-One "Trail Boss" 60T; Weber Kettle w/rotisserie ring; Big A$$ Rotisserie; Weber OTS; New Braunfels offset smoker.
Saddles BBQ Bistro