Pretty sure the new for '73 bumper "crash" standards were set at 5 MPH for the fronts and 2 1/2 MPH for the rears. So the front end got all those extra braces/brackets and the rear bumper simply got spaced a bit further from the body with these new brackets we're discussing.
Also pretty sure the the rear bumper guards were not part of the improved protection design, but were a "recommended" option. So they're commonly seen, but not all '73's had them. The March 15, '73 Dealer Accessorizer had the guards as option #732 V32 as in previous years. But were now noted as included with the Body Protection Group #334 Y95 which was not available on TA's.
|