A couple of things;
If you found a '73 Dart, the bumper is narrower and the mod for drilling your impact bumper shock brackets will look even better with the narrower unit. I'm not sure if the brackets from a '73 will work on a '74-'76, but you could check it out on your car.
'73 Plymouth has the same width as '73 Dodge front bumper and nearly the same profile, with a shallower peak in the bumper. You may try that first, before going with a bumper that contours a completely different grille profile ('67-'69 Dart).
I've never seen a '73-'76 Dart with a Plymouth Valiant/ Scamp bumper, but I would imagine that it would work better than a '67-'69 Dart bumper and give the results you're looking for, if not just trying a '73 Dart bumper and collapsing the shock mounts.
There is also an enormous reinforcement bar on the '73 that puts the bumper an additional 1/4" forward that can be ditched to also save an additional 35 lbs. Not sure if the impact bumper cars '74+ have them, but I know Amy's '73 bumper brackets bolt right up to the bumper without the reinforcement bar, with the same hardware.
Just a few things to consider.