Recommendation on removing rust from 1968 Mercury Cougar Roof?

The CCCA is for luxury cars of the 1915 to 1948 era. SO you perhaps need to move this to an area that would be seen by people who have cars of the same era .

Sandblasting it to a 'white metal' state is the best way to remove rust from steel on any car, classic or special interest.  It leaves the good metal in a primer-ready state, while removing and neutralizing the rust. 

Craig