The rear bumpers are in three groups. 70-72, 73, and 74. The brackets and bumpers will interchange as an assembly on the 70-73 cars. The 74 was changed slightly due to increasing crash protection. Dave you now need the 70-72 style bumper. You can drill new holes in your 73 bumper to use the older style brackets. I have done this and filled the extra original holes with bumper bolts that bolted to nothing.