I am not sure if it is the same for the seat belts, bur when I added the power vent windows the holes were there for attaching the motors but not the threads. If the same is true for the seat belt there is a tool that you can get that is kind of like a pop-riveter that allows you to install a threaded sleeve into that hole.

 

Yeah, I was wondering the same thing. Will the bolt holes be there under the trim and/or will I have to tap them. When I looked under the rear carpet there was no provisions for the third row since that wasn't an option on this vehicle. So I was wondering would the same be true for the rear seat belts mounts. I guess I'll be taking the rear trim off later today.

 

Not to mention the wells in the floor where the seatbelt attaches to the floor in the back.

 

Did you ever get your 3rd row seat in your non-3rd row Expedition? I'm about to try this, too and wondering what it's going to take.