You have a very similar axle to mine. Although you didn't mention for what year, for 1969 it would be:
BP = 2.73:1, non-posi, 10 bolt (standard rear end for base engine and Powerglide)
I would agree that 0403 is April 3
G = Detroit Gear and Axle Plant
2 = second shift
My axle code, for comparison is shown on the atached pic which decodes the same as yours except for date = Oct 18, 1968 (my car is a 3rd week Jan 69 build) and was built on the 1st shift instead of the second shift.