What valve springs should I use?

Why are we worrying about cracked Magnum heads? Seems like 80% of all Magnum engines are running around with cracks and operating just fine. I've got a set of ported cracked Magnum heads on a 420HP 360, thousands of miles of hard use with no problems. How many of you 'cracked head worriers' have ever experienced any water leaks from the cracks between the seats or any engine damaged from those cracked heads? Aren't the cracked heads coming off running engines for the most part. I've pulled a lot of 'em off wrecked cars/trucks and they had to be running to get in those wrecks. Just saying....cracked Magnum heads have never caused me a problem.