Driveline Hitting underside of floor (at rear)

Did you use the Hotchkis front hangers that come with the springs? If so, put the stock ones back on. If it is a Dart, 111" WB, it is to low. I wouldn't ditch the Dana for anything. I do know the Hotchkis springs suck with wrap, they will say they're fine but they are not. I made some Assassin bar knock offs for mine, I have probably 5" of clearance between the driveshaft and tunnel at rest but without some kind of traction bar, it will hit under acceleration.