Shouldn't be too hard unless you are wanting it to look like factory. Making patterns of cardboard and putting them in place. You can secure with pop rivits, sheet metal screws or get someone to weld it.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.