Spring supplier recommendation

[imarelic]

I have a 73 Z28 that I bought in 76. With the exception of the motor, it's in original condition with about 60K miles. Other than the shocks, the suspension is all original. The subframe bushings are shot, the rear multi leaf springs have broken leaves and are sagging badly. The motor has aluminum heads, aluminum intake and tube headers, so the front end is a lot lighter than stock. Sitting, the car looks like its being launched hard at a drag strip! It's gotten to the point were I'm scared to death to drive it aggressively. I've decided that it's time to get the suspension updated. Is there a supplier that you'd recommend, who can calculate the weight of the front end, based on the engine's lighter weight and sell me the correct front and rear springs to restore the proper ride height?