You'll burn the paint from the heat of a abrasive wheel grinder, been there done that many years ago. The casting is fairly thick, plus the horizontal ribs make it even thicker. There is no easy way to follow the curve at either end cutting through the ribs without some type of a burr as Keith has said, the burr doesn't generate as much heat as a cutoff wheel does. Opening up the casting isn't a fun job, and it's tedious.
Screwing up the finish on the opening, is probably why some of the castings got painted flat black after the paint got messed up during the project. The flat black spray bomb hides a multitude of paint sins......
