Should I call it quits?

The real value in that car is in 70 front end, tail panel and interior. It likely also has an 8 3/4 rear diff. Those parts are likely worth more than you paid for it. 73 up Dusters and Dart Sports are a dime a dozen. Find a rust free one and put the 70 parts on it. It will come with an upgraded front suspenion that you would have wanted for the 70 car.
Simple.
BTW post some pics of the whole car for us.