Steve,
All 68 Camaro Rally Sport cars (Coupes and Convertibles) got chrome strips on the front fenders, doors and rear fenders. They followed the contour of the indentations in the metal and gave the car a "Coke bottle" effect, as you can see in the first picture.
Non-Rally Sport cars (Coupes and Convertibles) got a singe chrome strip on the lower rocker panel as you can see in the second picture.
So to answer your question, yes, if the car's a Rally Sport, the rear strip should be slanted down.
Ed