Yes, it appears to be the correct rear axle for your car. Yes, the 1 after the G is part of the axle code and is interpreted as "first shift". PY1101G1 decodes as 2.56:1 axle ratio, non-posi, 12 bolt rear axle assembled on November 1, 1968 by the Detroit Gear & Axle Plant, first shift. The date also would be correct for a 12B built car. Congratulations!