This forum makes me laugh some times.
You laugh at the thought of it being refered to as structual. Well originally it was just a gearstick hole.
But its not original anymore is it. Its modified.
You take 1 big hole in the tunnel and then you make another big hole down a bit further.
Do you truely believe that it is not majorly weakened? Well now its twice as weak as it originally was.
Now think about the gearbox mounts. Most people just put it flat on the floor and put metal plates inside to spread the weight.
But you went one step further and welded mounts inside the tunnel.
Now where in relation to the old gearstick hole is the gearbox mounts. Roughly guessing with the size of the box, i think the new mounts would be under the original gearstick hole or under the new and old gearstick holes.
So being the top of the tunnel is weakened from the new and old hole, add the weight of the gearbox loading on the vertical sides of the tunnel, not the floor. Im sure that the structual integrity of the tunnel can easily be debated by the engineer.
Im actually suprised the engineer is happy with the new mounts. (are the welds painted?) If the hole is covered by a brased in peice of metal, what tells him the mounts are not brased on too?
As for pop rivets - engineers dont like them if they see them. They would prefer the plate be held in by nut and bolt rather than pop rivets.