I wouldn't use shackles to raise a car. It puts more stress on the leaf springs and can ultimately lead to them bending backwards. I've seen it on a lot of older hot rods with long shackles. The best way to raise one is a spring with more arch, like the SS springs, for example.
i have a pair of SS springs on it now probably 30/40 years old. Seems to not have much of an arch, I’d like to raise it about an inch. Shackles are almost straight up and down. 28” drag radials on it