Rear diff markings and codes.
That's the list I was thinking of.
Just noticed that it only lists 741 and 489 center sections. I suspect the 742 would be similar. I have a 742 from 12/66 with 2.76 gears and a Sure Grip has 2 yellow and 1 orange (from front to back) There might be a bit of white right before the yellow but not sure
