Solid STEEL ? There’s no rattling? .. I think the diff between my potential car and yours is yours is a Drag Week car and mine is jsta pure cruiser.

But after your post maybe the plan would be to try poly ORE make up some out of a hard rubber ...like a hockey puck.

The choice of a 4 link IS DONE and I don't think it would be worth the $$$ to change it to leaf springs.