Find a body then send it to the AMD Installation Center. I've sent 2 cars to these guys. They build the body just like GM would, everything is spot welded and assembled on jigs, the body literally looks like a brand new fresh body from GM. They have no problem doing mini tubs and subframe connectors during the rebuild process, heck they even did the mods for the quadra-link on the last one for me.
http://www.amdinstallation.com/