The sawzall will work great on the rock rails. However, the pinch seam might be a little more of a challenge. Depends how far back the blade goes and what is behind to hit.

I prefer a metal cutting wheel on my right-angle grinder, but that will have its own challenges because of the curves around the pinch seam.

Just mark everything good so you get straight cuts.

An old carpenter's saying I often ignore (and regret when I do): "Measure twice, cut once!"

 

I just finished chopping mine - woo hoo! Looks great. I did one good thing and two stupid things that are worth sharing:

Good thing: I put an 8" metal cutting blade on my good miter saw, and it made short work of the rails. Went through them like butter and left a perfect edge needing no cleanup. Plus it provides a groovy Fourth of July show during the cutting. :-)

Stupid thing #1: I marked the cuts with masking tape and left it on when doing the above cutting. It got so hot that it melted the tape into the existing paint, which left a grimy mess that had to be scraped off, including the existing paint.

Stupid thing #2: After slicing off the sheet metal with a metal cutting blade on my recip saw (again, super easy and went through it like butter), I plugged the gap with silicon like someone suggested. Do this AFTER you spray on your black primer. I did it first, leaving some silicon residue on the surface to be painted.

 

I think Lorena said the same thing...

 

I don't have the Rubi, but I did trim the pinch seem on my X to clear my 35's better. I just used a dremel tool. It cut right through it with no problem, plus it was small enough that I could cut the angle exactly how I wanted it and had plenty of room to maneuver with it. I then used touch up paint I got from the dealer for my Jeep color, and painted over the bare metal so I don't have to worry about rust.