On my dad's car we welded in the front sub from a '79 Trans Am. Also, I think RBs (or something like that) makes a front sub that uses G-body or F-body parts. It's also a weld in. We looked at it, but felt that it dropped the front too much.
Shiny Side Up!
Bill
'72 442 "Inamorata"
www.FQuick.com/ProTouring442