Supposedly the Buick 350 weighs about 450 lbs vs the V6 at 390 lbs so about 60 lbs more. I currently don't have a winch, but I have nothing in the back at the moment besides the roll bar. The Pro Comps on my 69 sit pretty close to level with a v6, no winch, hard top, and tire rack with fuel cans. The back sits noticeably higher when the hardtop is off. At some level since they aren't making custom springs for a particular rig they have to target the most common use case. At least shackles are easy to swap out.