Engine 1989 Gt vert stock heads valve spring help

You don't need to change out the valve springs to run a B303 cam as it's only .480" lift. You do have to do a lot work to change it out and it's really not going to give you much of HP boost without updating the heads and intake. If you could find a set of GT40 heads and Explorer intake that you could install while you are at it, you could pick up some decent gains and people almost give that stuff away.