Orchidskip,
I don't know if the shackle frame mount is original, but if it's riveted it probably is.
I don't think the 1/2 and 3/4 ton trucks had the shackles pointing down and the springs under the shackles. That was on the 1 ton and up trucks. What happens if you turn your shackles up, and mount the spring over the frame mount? Now you'll have all the movement that you would expect. I believe that's how it should be done.
I hope you havn't buggered up your mount or your shiny new springs in the process.
Good Luck!
