Unless you find NOS SS springs that were made in Canada or the US, the springs out there now are nothing short of junk. Even the so called pro-stock springs that are distributed by reputable sources sagged after a year or so. At that point, you're better off with a HD truck spring.
Go with the launchers, made by Greg Luneak at Tri-city in California as I have and you'll never go back to the off shore crap supposedly called SS springs.