As I'm not a big fan of making holes in my 71, I was thinking about using a strong magnetic leaf (80g/cm² = 0.44oz/inch²).
Will it be enough, or is ther a risk to lose my panel during driving?
They make a pretty strong neodymium magnets. The basic is to not get any air under the panel or it will act like a sail and fly off at higher speed. Think aerodynamic and spoilers.
It would work but not as well because it would be behind glass. Also reducing the effectiveness would be the vertical angle because it would not be facing the direction of the sun very much.
It could also get very hot in that position and perhaps could be a bit dangerous as a fire risk IMO.