James, thanks for the interesting pictures. My blue car was Nor built 11A, car is all black underneath except for just below the firewall and forward 6" of the floor. That area is grey primer. Ignore the orange repaint in pictures. My frame rails looked grey also but I took a scotchbrite pad to them and it was black underneath the grey. I thought maybe they are galvanized steel and the grey coming thru was do to the zinc. It only showed up on the rear frame rails and the square box at the front of the rail. My floor looked just like your Blue Z, but not so nice. Had the same blue overspray on the lower ribs, wheel wells, trunk pan etc. The interior of the black car shows allot of red primer before the grey primer and paint, where on my car the red was covered up more but still visible. I just got my car out of the paint shop and trying to decide if I should attempt to duplicate the grey primer & runs on the front floor. The paint ran out of the seam and scallop cuts under the toe boards. We are thinking the paint guns were cleaned out and sprayed into pockets for the sub frame mounts. It shows signs of black and grey paint leaking out. Looking for an opinion and or advice at this point. George