Believe it or not....I have used Easy-Off oven cleaner on a 65 chevelle rear once. It took lots of elbow grease & steel wool, but it was sparkling clean when I was done AND the factory paint daubs were still intact when I was done. might take some soak time to remove heavy crud or factory black paint. The bare iron flash rusted almost immediately, but overall, it turned out really well. It appeared to me that the '65 rear was never painted from the factory. Just paint daubs on bare cast iron. Make sure you rinse thoroughly, I mixed a little baking soda in the water to make sure the lye was neutralized & wear gloves & eye protection.
Since then, I got lazy & just sandblasted & painted or powdercoated the rears I have done.