These days, most serious builds and those that need to have an SFI tag are all round tube. And it's 4130. 1.500x.065 frame rails but there is also plenty of diagonals and bracing as well.
Agreed,two different style builds. Those that are milder using the body and cage as one structure. And those trying to be as light as possible being 25.5D compliant. The sheet metal is merely visual and not much structure. Doug
