i looked into this when i brought a second hand bumper, just to check difference between airbag and non airbag bumpers.
Basically the ones for models with airbags have a crumple zone built into the mounting to enable the sensors to activate. I fitted non airbag to mine, but it is a 95 300, and who knows if they work on it anyway, and since buying the srs light is on anyway. :doh: