You've got way too many leaves in that spring. It was built to hold up something like a much heavier 48 Ford so it will ride like a rock unless you soften it up some. I would remove every other leaf after leaving the main leaf and the leaf next to that one. Start there and see how it sits and bounces.
I count about 12 leaves. Get it down to 6 or 7 and you will have a good start.
Don