Sorry...stepping into this sort of late, but have you counted the spring leaves on both sides? They must be equal. Also if you remove the springs the length (eye to eye) must be the same. If the eye to eye length of one is shorter than the other, it will cause that side to sit higher...but unless the difference is small, I think you would have noticed this when you installed them. The number of leaves can get overlooked, though. And if one spring was put together with fewer leaves, that side will sit lower. I don't have data for the 1956 truck, but I'm almost certain it had 6 leaves in the front and 7 in the rear.
Jon
