Several manufacturers are now producing aftermarket frames for GM A-Bodies from '64 through '72.
https://www.artmorrison.com/chevelle.php
This would be a tremendous project. There is no way I could do it myself. But this would be keeping in line with my quest to spend $300,000 to have a $30,000 car
Jackie, I've been eyeballin' those.
They make a lot of sense for a Pro Touring rig like your Chevelle. -Al