It’s not the shackles. The factory shackles are also 4” center to center on the pivots.
You can probably shorten them a little, but you’ll run into interference issues before you lower the car all that much. I replaced my rear shackles with spring sliders, which are quite a bit shorter, and that only lowered the car about a 1/2”.
Which super stock springs are those? How many miles are on them? They should settle some as they wear in, but that will take time and miles.
