I once installed a 'junkyard' rear sway bar in my V70. It went in OK and it improved handling. I never measured its diameter.
Give
www.ipdusa.com a look. They say their sway bars (anti-roll bars to y'all) are their signature item.
There's a 3 panel, rotating message at the top of their homepage. One says, "Ask IPD". Go there and ask what you like. They are a good company with engaged people.