I just test fitted my floor pan. Looked good except the piece I will call the "backbone" is way to high (1/2") keeping the back of the floor pan from touching the flat seam where it meets the trunk pan. This piece is a half circle piece that supports the rear of the tunnel. Has anyone else had this issue?

Photo of the "Backbone"

I had the same problem. I drilled out the spot welds on the rear pinion snubber holder and cut, welded , and reshaped it. I think I also cut a few relief cuts in the floor pan in the tunnel area to make it fit better. I have heard of others having the exact same problem.

I think you can see two cuts in the tunnel area that I made to shrink the tunnel up.

Same problem on my 69