73 roadster mounted on a plinth ...

... with 1 1/4" self-tapper screws into nylon sockets. No insulating sheet or spacers.

V8 no plinth - what looks like a plinth ...

... is an insulating sheet between the fusebox and the spacers. 3/16" UNF screws (note the lower one is sheared) into welded nuts on the back of the inner wing.

V8 screw is 1 1/2" long, the rusty part is all contained within the nut, it does not protrude beyond it.