I would move the springs inboard and mini-tub the car.
I would consider a full tube chassis car before I back-halfed a mopar, when converting to tube chassis the largest weight savings can be gained in the front half of the car (where you need it!) than in the rear half on car.
If you go to Alston website they discuss this in detail.
Bob
PS: a 500 hp car with a 10" tire is noramally faster than a 500 hp car with a 14" tire just because it takes more hp to rotate big tires!!