It prolly came loose because your cam has way more lift than your original setup. I built a big block 2 years ago & had the stock rockers come loose twice while test driving the truck (2 different cylinders within about 100 miles of each other). The cam was a mild cam, but the stock rocker nuts found a way to come loose. I put polylocks on it & never had a problem. It’s cheap insurance (especially with your setup - soo much work to take the intake off, if a pushrod falls out of position). It could cause damage as well. I think polylocks are about $35-45 for a set.