16 ga. is going to be awful stiff to try to form. Our local auto parts store used to have 18 and 22 ga. sheet metal, but their source went out of business and they can't find another. SO, I'm cutting up the rest of the trunk lid I used to fix the lid on my 66 so I have metal to work on my other car. I think 20 gauge is what they used. If you can't find sheet metal, find an old trunk lid or other body panel in a salvage yard to fabricate pieces.You might have to resort to some 16ga steel panel and cut what you need.