The only thing that would be lighter would be the torsion bars, and that weight difference would be probably less than a pound. The radiator will be slightly smaller, but, if you put in a healthy big block, you'll probably need to upgrade the torsion bars and rad, so you're right back to the same weight as any other A body. All other front end parts weigh the same regardless of the engine size.
i agree, i dont think the weight of the suspension makes any difference, my dart has all of the original slant six stuff up front and a big block and it doesnt pull the wheels, pulling the wheels with a big block is more an issue of traction imho..