[Barrier Blue]

Larry
If the nuts are welded to the floor, you may have problems with aligning the bolts.
What I did was just put the new bushings in place, run the bolt up thru from below, and have someone work the nut down on the bolt from above, then just tighten it down. make a sheetmetal patch and put small sheetmetal screws in to hold the patch down, with some silicone sealer around the edge.
That way, if you ever need access again, you won't have to cut again.
If it's in an exposed area, and don't want to see the patch, put some bondo on it to hide it.
Hope this helps.
Jeff