Yeah since you are cutting out your floor anyways, I would just get to cutting. I have also done this before on my truck on two different bolts. The first cab was going to be scraped to I just cut a hole in the floor, but the second cab was a keeper so I just drilled 2 1/2" holes on either side of the channel exposing a small area of the lug that was spinning inside the channel. Mig at full voltage and filled the hole with weld to re-weld the lug to all the surrounding material, and it has held every since. Then just sand or grind down smooth and primer and paint.
Remington