My 70 dart thinks she's fat.

Replace the front fender inner shields (sheet metal shield that keeps road crap out of your door jambs) with shields from a 73 or later Dart (2dr, 4dr, sport - it doesn't matter). They changed them to plastic when trying to save weight for gas mileage.
Make a door window set up like the 68 hemi darts - use seat belt material to pull up and hold the windows in place with a snap at the bottom of the inner door and ditch the heavy window regulators. For the back windows, fix them in place and dump those mechanisms too (how many folks are going to be in the back seat of this anyway???) And speaking of back seats, dump them and carpet the back seat area.

Somebody here makes light aluminum bumper bracket for your "for show only" fiberglass front bumper
I have some thin .011 aluminum I could make something for those I think.