Re: WOW ... stop the rust while you can ...
In my experience restoring cars, I would then treat it with a rust neutralizer solution and then repaint.
If it is not done you will be back doing it again. As I remind my self all the time, do it right the first time.
Joe
PS restorations include- TR3, TR6, MGA, MG TD so I know a little about rust with those old British cars.