distributer cap mods?

If you are breaking 5/16 studs at 20 ft lbs, then that means they are probably stretched to their limit at 15. You need to throw away all that Ching Chang hardware you're using and buy some good fasteners like ARP brand. Edelbrock has installation instructions on their website. They recommend 25 ft lbs in a specific pattern. Get a new gasket and good hardware, follow Edelbrocks procedure and your problem should be solved.