You want a stiff spring in the rear, and a soft spring in the front. Use the stock V-8s in the rear, and the 4cyl's up front.
It sounds to me like all you need is some weight transfer and some tires. Oh yeah, and a tranny.

I drove my 94 all over hell with a 2600 convertor and I got 20mpg on the interstate. I'd have to do 80mph to keep the convertor above its flash speed, otherwise the trans would get hot.
Andy