Body panel adhesives

On the Dart Lite and Feather Duster models, how did they attach the aluminum substructure to the hood skin and deck skin? Was it some kind of epoxy or rivet or what? I don't think it could be welds.

On all-steel hoods, were the substructures welded or attached similarly? I don't see welds any where, except at the perimeter on an all steel hood.

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Do any of the body folks here have a recommendation on something that could be used to do something similar?