Demon/Dart molded in fender extensions?

'72 has pot metal extensions which vibrate at a difference frequency then the sheet metal the fenders are made of, '70 and '71 are composite and also vibrate differently, anyway what I am tiring to say is it will crack over time. If you must do it try using panel bond, it's a two part epoxy used for gluing cars together where you can't weld. Don't forget to scuff it to give it something to bond too.