8 3/4 rear casting 1820657

My 67 Dart 340 hybrid has 8 3/4 rear, type 1820657 (58-64). It acts like a non-Sure Grip (wheels don't spin in the same direction when off the ground). The gear ratio on these units is stamped into the case toward the back, on the opposite side of the casting numbers. The numbers stamped appear to be 3.58 (no "S" for Sure Grip). As far as I can tell from what I've read and known about, this ratio does not exist. It probably would be a 43/12 gear set, but I haven't taken it apart yet. Does any have knowledge of such a ratio?
Author: admin