The 78-81 Malibu coupes and the 78-80 sedans have a very large shelf which is also shared with the Pontiac Lemans/Grand Am of the same years. The 81-83 Malibu sedans as well as the 81-86 Pontiac Lemans/Grand Lemans and Bonneville have a smaller package shelf that is similar to the 78-88 Monte Carlo, Regal, Cutlass, Grand Prix coupes. I am not sure if they interchange though.