Lots of options if you've got junk vehicles around, or a scrapyard nearby. I buy all sorts of useable steel remnants and scraps from a local yard that I figure I can make work on my builds. Of course I toss anything I tear off a car in a scrap pile behind the shed and search there also when I need to fab anything.
Pieces of old frame rail make good material for brackets, mounts, or gussets.
Mine's not much of a '63 Falcon anymore either!