[sick472]

The two narrow sill plates that are visible through the wheel well do not bolt to the frame.

As far as the width at the tailgate goes. One truck could be slightly different from the next and you should determine that by preassembling the tailgate to the bed to find out what you bed wants. I'd hate to measure mine to find out yours wants an 1/8" more or less...you would not be happy.

I converted my steel bed to wood from scratch, no kits as I was on a budget that allowed more time and less money. I squared the bed up without installing the wood and by having the tail gate installed. To do this, I took careful measurements from the front left corner to the back right corner and compared that to the opposite measurement (front right to back left). When those two measurements are the same, the bed is squared up in itself. Then you want to check the widths about every foot or so from front to back to make sure your side panels are straight. The width at the front end of the bed should be very close to the width at the tailgate. Some slop is available at the front panel to finesse the width, but not much (maybe a total of an 1/8" when both sides are adjusted all-in or all-out...a 1/16th per side).

From there you need to align the bed to the cab or vise versa, which ever needs shifted, or both. I would max out the slop, in your case, so that the front of the bed is as wide as you can get it, then center the bed with the cab, then inspect to see if your bed to frame mounting holes line up well enough to get it bolted up. If not, look at moving the cab and front clip...or inspect for a bent frame.