Has anyone ever done a hardtop to ragtop conversion? Is it possible? What would be involved?

Changing the Frame, Cutting the top, Modifying the body to accomodate the convertible top, etc. You would probably have to find a donor car for all of the conversion pieces. It might be cheaper and easier purchasing a project convertible and changing body panels and floors as time and money permit.

I had a friend do it with a 66 Buick GS. He had a rusty convert, and found a rust free hard top. He cut the top half off each one and swapped the convert onto the ht body. Every part needed for the convert was removed and replaced. You would never know by looking at it. He also boxed the frame exactly the way the factory did. It took him about 10 years, off and on.

Think about it.You can purchase any part from the firewall all the way back to the trunk floor for 68-72 chevelles so even if you have a really rusty convertible you're still ahead of the game.plus the main floor section and the trunk floor are available as assembled units,so your time spent on the car will be reduced since your not piecing parts together.