64 Dart

I got frame connectors with a floor profile, but after pulling out the carpet found out I don’t have a floor, so i used 2x3 square tube and did cross bars for the roll cage main loop. I will have to redo the whole floor probably will use sheet metal and transmission tunnel.
Should id floor first and then cut out transmission tunnel or transmission tunnel first? Also any advice on it will be super helpful, i got a 18ga sheet metal.
Thank you!!

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