Need to stiffen my rear 68 dart suspension

if the rear springs are just plain worn out he may need those as well.

I have a Hodgkis sway bar front and rear but I need a stiffer leaf spring. Track car so dont care about bumpy ride on the street and raising the car an inch would be a plus!!!

What about using the "add a leaf" JC set-up to try it.
Do you guy's think i would be waisting money.
The back end of my car is scooting out in the twisties. I need to plant those 315 rear tires more firmly. The front end has all HD everything including aftermarket A a rms but only sway bar and Wilwoods in back