Car is a 69 Coronet R/T convert. The car has Dynamat and Dynapad installed throughout the car. The trunk has been completely boxed in with carpet and extra insulation for sound deadening. Even with heavy duty NEW rear leaf springs, the car sags. The springs are almost flat. I am sure that it is from the extra weight (estimate 500-600 pounds). What would you suggest to improve ride height and handling.