8 vs 10 on idle doesn't really matter with respect to making it shake like a leaf intermittently. I also believe factory/Chilton's timing specs are of no value with modern fuels and presumably an engine that has been rebuilt at some time in its history and has a different compression ratio than stock. Regardless of timing I think you're looking the wrong direction and changing timing is not going to solve the actual problem. Sounds like an intermitent misfire which would have me looking at plug wires and/or distributor cap/rotor contacts. Maybe even idle mixture or idle speed issue. Do you have a tach on the car? Can you tell if RPMs are simply dropping a litle bit too low when the shaking starts at a stoplight? Does shaking stop if you take it out of gear, allowing RPMS to raise up a little bit?
