Johnny,
Was your '74 a Dart Sport or a Dart Swinger/Custom? All of the '74 Sports and Dusters I've ever seen had the regular bumper brackets. I haven't seen enough '74 Swingers/Customs to be sure. '75 & '76 all had the shock-style brackets.
My dart is a swinger, and a 74. Still have the car. Lol. I never would have thought a sport and swinger would have different mounts, but I also wouldn't have figured the brackets changed between 73 and 76.
Clearly im a learnin something new.
However, for 100 percent certainty, my 74 swinger came with the shock type bumper mounts. I replaced the oe bumper with a fiberglass unit. Thats why my oe is not on the car.
Again not positive if im adding anything here, just offering up a 74 bumper, from a swinger, if it helps the op for reference.