I recently picked up a 68 tempest with a non-original late 60's 350. There is considerable valve noise on the drivers side. I removed the cover and found 1 out of all the rocker nuts a little loose. I tightened it down like the others. Didn't seem to help much. From what I have read, I must have the "net lash" system. Can anyone recommend the next steps to solving the noise problem?