When I repaired my floor in that area, I tried to use the inner fender to locate the holes from the outside, but missed a bit. It was a giant PITA to get the bolts started in the weld nuts on the inner fender. I don't think I'd recommend that approach, or at least do a better job than I did. I could measure mine, but you probably wouldn't want to use those measurements.
Hopefully another bolter will be able to do that for you.
