You only get so far with cleaning solutions and ultrasonic cleaner on a 50-year-old cast aluminum piece. Tumbling in a professional manner with proper media, or glass bead blasting is the only way to get a more correct finish and getting off the hard gunk. Any solution you put a carb in you need to look for the reaction, if you get heavy bubble gassing you need to remove it immediately. Even those brightener's and such do not actually brighten and are only soaked for 2 minutes for a passive coating.