1" Sway Bar

Can't say from experience but probably not much, I'd replace all the sway bar bushings and end links with polyurethane first so the stock bar is actually working the way it's supposed to. I did that to an '88 5th Ave M-body and it made a big difference with the stock sway bar. Some aftermarket bars also have different mounting/connection points so even if the diameter is similar it still may reduce sway more than a stock piece.