i just removed an original dec 69 built l.a challenger shield to fix the sender float and the bolts on that were longer with a self cutting end like a tex screw-they were 7/16 head with 1/4 unc thread about 1 1/4 long at a guess. if this question was last week i would have taken a picture. if no one else chimes in with a pic i`ll see what i can do. shields were also installed prior to proof coating.
all the best
frank.