DICK RUZZIN
I have Konis specifically designed for the Mangusta. I bought them in 1972 and had them rebuilt in 2007. I am sure they can put a set together for you. They are adjustable to refresh them, not change the valve rate. They are coil-over, adjustable in the rear but not in the front. You adjust the compression of the rear spring to raise or lower the rear of the car, that also makes the rebound stiffer or softer. The thing to do is to match the rear with the front in impact. Shocks are the foundation of safe handling, that is the place to spend money.
Why does he need new springs? It is a big engineering project to change spring rates, it is all trial and error with subjective evaluation.
My car ride impact is the same as my 2005 Corvette, which is quite comfortable. My tires are Good Year Eagle 275X15X60 in the rear and 235X15X60 in the front. I am going to sell them and change the front size to 225X15X60.
Call me if you want more info,
DICK RUZZIN, 313-824-0539.