I have a 1967 Convertible 11B NOR build with casting 3841177 rear drums that I believe are original to the car. Amazingly one of the drums has only been turned 0.020 while the other has been turned 0.080. I'd like to get another brake drum to replace the 0.080 turned one. A friend has a couple of brake drums supposedly off a 1969 Camaro with casting 3993560. Are these the same? I haven't looked at them myself but in pictures I've found it looks like the 3993560 is the same but has the max dia cast as 9.590. The 3841177 do not have a max dia cast in them. Anybody have any comments about the difference in these brake drums or brake drums in general and how this difference in size (0.020 vs 0.080) might affect braking?