This may be stupid, but is there a reason you can't fiberglass it on to the hood? And then sand down the excess fiberglass used to mount it. I once repaired a steel hood with fiberglass. Someone cut a 3" hole in the hood right over the carburetor, so I cut away the rough edges, sanded it down, and fiberglassed over the hole. I then finished sanded top and bottom, and unless you were to run a magnet over it, you wouldn't even know the hole was there.
I intend on doing something similar with my 66. I have a bond on shelby scoop, and I plan on cutting a hole in the hood and building a ram air style hood scoop retro the 65 shelbies.
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