I don't remember how it was attached at the drip rail area...I do remember that underneath the stainless moulding at the belt line was a long row of pop rivets holding the "new" sheet metal to the body lower panels. However it was welded and metal finished where it curved around the back of the car. Here is a link to Barry Cawley's Delivery wagon. He will be at the Mopar Nats this weekend, I am hoping to see him there!
http://blogs.moparmusclemagazine.com/6739274/miscellaneous/ppg-goodguys-plymouth-valiant/index.html