The Gen III dash area is completely different from all previous generation FJRs. The current N-Line Dash will not fit the GenIII.
A re-design is unfortunately required, and it's going to be challenging for the fabricator, because there are only four (4) hard mounting points in the dash area, and they are laid out extremely poorly as far as mounting a dash is concerned. Further, the remaining four hard mounting areas are not really load-bearing attachment points.
And the biggest drawback? The forward hard mounting point (under the windscreen) of the Gen I and IIs is no longer present on the GenIII. This is a huge loss... fabricators are going to have to get pretty dang-gone creative here, I think.
If he didn't live clear across the country from me, I would donate my GenIII to garauld for a week or so, and see what kind of magic he can come up with...