Slicks to Leaf Spring Space?

The section width of the tire is the issue...and the section width depends on the width of the rim it is mounted on....short answer is, I don't think you will have sufficient clearance when the tire is mounted.

If your rim is 3" from the spring and IF your section width on your tire is (for example) 10.5", then you will have 2.25" sticking out on each side, so only 3/4" clearance. I would get a wider rim if possible.

I like to have a minimum of a fingers width around the tire, which for me is about an inch (run your hand around the tire and not have it touch the spring).