Congrats smvijayan, your ss80 really looks good. Even though it has a good amount of rust it does not look bad at all considering the car was in Chennai and the age.
about the patch work you are planning to go is a good idea, but make sure your painter matches the paint shade with the old original paint on the car cos the fresh François white shade will look new when compared to the other body parts.
also try to find a original side mirror, i am telling this cos i see you live in Singapore right now and it shouldn't be hard to source the same there.