They are 70's cars, I think shackles are period correct and will look very kewl on your Mav. yes it will make her a little skiddish and a little less safe, but if that's your look man then I dig it. Let it roll. Moog makes some I know but if it is temporary and just for some 70's thing find some and put them on.
They didn't look cool in the '70s and they don't look cool now. They are a cheap, unsafe way to raise the rear of a car. It irritates me when people are too cheap to replace fatigued leafsprings. I'll bet many of them have big-screen HD TVs, cable or satellite dish, and fancy cell-phones, but can't come up with $200 for some dang springs. Just save up the money and do it right.