Q's on installing tube bars for an 01 DC

Hey y'all. Picked up a pair of black tube steps for my baby a while back and I've finally had time to get to installing. BUT, the install has me somewhat confused. First, the new bars use only two mounting points, front and rear; no middle mount. I can get with that, but the part that I'm fighting with is mounting. It's showing that I use the original chassis bolt. However, my original chassis bolt isn't anchored from the top and rotates when I unscrew / screw the bolt holding it on. Is there a way to hold it from the head? Is that under the carpet in the cabin?

Also, I'm having a dickens of a time fitting the 3/8" bolt set (nearest the chassis bolt). Any tips on holding it in place?

Lastly, should I be concerned that it's only mounted on two points instead of three as the OEM step is?

Here is an album of the instructions as well as pics of the areas of install.