What suspension do you now have in the front. Chevies of the late 30's early 40's used I beam straight axles, Knee action with coils, and also the double A arm more modern design. There are kits to bolt in mustang II fronts, the frames are a little different for different stock suspensions used. and what type of rack does the caddy use , GM used both center pivot and conventional shorter link racks in those years. There is a Wiki article here on hotrodders about upgrading the larger Gm cars of that era, buicks olds pontiacs, most parts are different but will give you some ideas.